Natural Disasters Midterm
ENVS 219: Natural Disasters Exam 1 Study Guide
Lecture concepts to know AND understand are below. For the readings, you should have a general idea of the name/date/location of the disasters from the readings, plus key concepts mentioned in the readings. You don’t need to know other specific details from the readings.
Lecture:
Day 1 Intro 1.
• Which disaster types were most deadly globally between 1900-2020? Which disaster type has
been most deadly in the United States?
Lecture: Plate Tectonics 2.
• What ideas support Wagner’s continental drift hypothesis?
◦ Puzzle-Like Fit of Continents – The shapes of continents, especially South America and Africa, fit together like pieces of a puzzle, suggesting they were once connected.
◦ Matching Rock Sequences & Mountain Chains – Similar rock formations and mountain ranges exist on continents that are now separated, indicating they were once part of the same landmass.
◦ Glacial Evidence in Tropical Regions – Marks left by ancient glaciers were found in areas that are now warm, meaning these regions were once much colder and likely part of a supercontinent.
◦ Fossil Distribution – Identical fossils of plants and animals were found on continents that are now widely separated by oceans, showing that these landmasses were once connected.
• Be able to name and describe the 6 pieces of evidence that support plate tectonics/ seafloor spreading (patterns and how this supports the theory)
◦ (1) Seafloor Topography: Mid-ocean ridges (underwater mountain ranges) are found in the middle of oceans, and deep trenches are found near some continental edges, showing where new crust is formed and old crust is destroyed.
◦ (2) Age of the Seafloor: The youngest rocks are at mid-ocean ridges, and the oldest are near trenches, showing that new seafloor is created at ridges and moves outward.
‣ New rock is made at the ridges, and old rock moves outward.
‣ The age pattern of the seafloor (youngest at the ridges, oldest at the trenches) shows that the ocean floor is constantly being made and pushed outward, which is how seafloor spreading works!
◦ (3) Heat Flow: The highest heat flow is at mid-ocean ridges, where magma rises, and the lowest is far from ridges, supporting new crust formation.
‣ When the magma rises to the surface, it brings heat with it. So, the areas at the mid-ocean ridges are hotter compared to other parts of the ocean floor.
‣ This higher heat flow at mid-ocean ridges is an important piece of evidence because it shows where new crust is being formed as magma cools and hardens.
◦ (4) Volcanoes: Most volcanoes are located along plate boundaries, especially around trenches, indicating magma activity where plates interact.
‣ Subduction zones are a key place for volcanoes because they are where plates sink into the mantle and create the conditions for magma to form and rise.
‣ Volcanoes are often located around these trenches because they mark where plates are interacting and where magma is generated.
‣ The fact that volcanoes are found around plate boundaries, especially near trenches (subduction zones), supports the idea that tectonic plates are constantly interacting with each other. These interactions lead to the formation of magma and, ultimately, volcanoes.
◦ (5) Earthquakes: Earthquakes are concentrated at ridges and trenches, with the deepest ones near trenches, showing plate movement and subduction.
‣ Earthquakes happen where plates interact—especially at ridges (where plates pull apart) and trenches (where plates collide and one sinks under the other).
‣ The deepest earthquakes are found near trenches, showing that the sinking plate is causing intense pressure and movement in the Earth's crust.
◦ (6) Paleomagnetism: Magnetic minerals in seafloor rocks record Earth's magnetic reversals in symmetrical patterns on either side of mid-ocean ridges, proving seafloor spreading as new rock forms and moves outward.
‣ The Earth's magnetic field flips because of changes in the movement of liquid iron in the outer core.
‣ when new rock forms at mid-ocean ridges, the tiny magnetic minerals inside align with Earth’s magnetic field at that time. Over millions of years, this creates symmetrical stripes on both sides of the ridge, proving that new rock is forming and spreading outward
• Know the differences between the lithosphere and asthenosphere
◦ lithosphere: crust and very upper mantle there plates are
◦ asthenosphere: 1% melted minerals liquid moves plates flows
• Know the 3 main types of plate boundaries (including divergent stages, subtypes of convergent, etc): what happens to material at each boundary, what types of features are present (and where they are located), which way the plates move relative to each other. Be able to provide an example location of Earth for each type of boundary.
◦ Divergent boundaries occur where two tectonic plates are moving apart. At these boundaries, magma rises from the mantle to create new oceanic crust, forming mid-ocean ridges. As the plates move apart, features like rift valleys and volcanoes can form. The East African Rift is an example of a divergent boundary where continental crust is breaking apart, and the Mid-Atlantic Ridge is an example where oceanic plates are pulling apart.
◦ Convergent boundaries occur where two plates collide. At these boundaries, one plate may be forced beneath the other in a process called subduction. The three subtypes of convergent boundaries are:
◦ 1) Oceanic/Oceanic - One oceanic plate is subducted beneath the other, forming deep ocean trenches and volcanic arcs, like the Mariana Trench.
◦ 2) Oceanic/Continental - The denser oceanic plate is subducted beneath the continental plate, creating features like ocean trenches, mountain ranges, and volcanic arcs, as seen at the Andes Mountains.
◦ 3) Continental/Continental - When two continental plates collide, neither is subducted, leading to the formation of large mountain ranges like the Himalayas.
◦ Transform boundaries occur where two plates slide past each other horizontally. These boundaries often cause earthquakes due to the friction between the plates. The San Andreas Fault in California is an example of a transform boundary.
◦ At each boundary, the movement of the plates leads to different geological features and processes, such as earthquakes, volcanoes, and the formation or destruction of crust.
Lecture: Earthquakes
• Know the difference between focus and epicenter, the 3 fault types and what types of boundary each is commonly associated with, and how earthquakes occur related to plate tectonics
◦ Focus is the point inside the Earth where the earthquake begins, while the epicenter is the point on the Earth's surface directly above the focus.
‣ Focus = The exact point inside the Earth where the earthquake starts.
‣ Epicenter = The point on the surface directly above the focus (where shaking is usually strongest).
◦ There are three main types of faults:
‣ strike-slip faults, where blocks move horizontally (transform boundaries)
• Strike-Slip Faults → Transform Boundaries
•
• Stress Type: Shear stress (sideways pushing)
• Why? At transform boundaries, plates slide past each other horizontally, which creates strike-slip faults.
‣ reverse faults, where the block above the fault moves up (convergent boundaries)
• Reverse Faults → Convergent Boundaries
•
• Stress Type: Compression stress (plates pushing together)
• Why? At convergent boundaries, plates collide, forcing one block to push up over the other.
• Example: Himalayas (continental collision), Andes Mountains (subduction zone)
‣ normal faults, where the block above the fault moves down (divergent boundaries).
• Normal Faults → Divergent Boundaries
•
• Stress Type: Tension stress (pulling apart)
• Why? At divergent boundaries, plates move away from each other, causing the block above the fault to drop down as the crust stretches.
• Example: East African Rift, Mid-Atlantic Ridge
◦ Earthquakes occur because of the stress and movement of tectonic plates. These movements are caused by forces along plate boundaries, and faults form as a result of these forces. The movement of rocks along faults can cause earthquakes, with the stress building up over time until it is released suddenly.
• Know the difference between recurrence interval and seismic gap, and how each contributes to the understanding of earthquake risk.
◦ Recurrence interval refers to the average length of time between two events, such as earthquakes, on the same fault. It helps scientists estimate when future earthquakes may occur based on the historical frequency of past events. Larger earthquakes tend to have longer recurrence intervals, sometimes spanning centuries, while smaller events may occur more frequently, even within decades.
‣ Recurrence Interval (When might an earthquake happen?)
‣ Definition: The average time between two earthquakes on the same fault.
‣ How it helps: By studying past earthquakes, scientists estimate how often quakes of a certain size occur in a region.
‣ Example: If a fault has had a major earthquake every 150 years and the last one was 140 years ago, another may be due soon.
◦ Seismic gap refers to sections of active faults that have not experienced recent earthquakes despite being in areas prone to them. These gaps indicate potential sites for future earthquakes because the stress needed for fault movement has likely built up but not yet been released. Understanding both recurrence intervals and seismic gaps is crucial for assessing earthquake risk and preparing for future seismic events.
‣ Seismic Gap (Where might an earthquake happen?)
‣ Definition: A section of a fault that hasn't had an earthquake in a long time, even though other nearby sections have.
‣ Why it matters: This means stress is building up in that area, making it a likely location for a future earthquake.
‣ Example: If a fault has had earthquakes every 50 years along most of its length, but one section hasn’t moved in 200 years, that section (seismic gap) is a high-risk zone.
• Where are the most earthquakes found in the US? Where do they cause the most damage?
◦ The most earthquakes in the U.S. are found along the convergent plate boundary south of Alaska, especially in Alaska itself.
‣ Alaska has the most earthquakes in the U.S. This is because it sits on the convergent plate boundary where the Pacific Plate is being forced under the North American Plate in a process called subduction. This creates a lot of seismic activity, including deep and powerful earthquakes.
◦ The most earthquake damage in the U.S. typically occurs in populous California, particularly around the San Francisco Bay Area, where there is a 62% chance of a large earthquake by 2032.
‣ California, especially the San Francisco Bay Area, experiences the most damage from earthquakes. The San Andreas Fault and other nearby fault lines cause frequent, strong earthquakes. Since this area is densely populated, earthquakes here can lead to significant destruction.
‣ There is a 62% chance of a large earthquake (magnitude 6.7 or higher) in the San Francisco Bay Area by 2032, which highlights the potential risk and damage in this region.
• Know the differences between the 4 types of seismic waves, including where they occur and how they move
◦ The four types of seismic waves are P waves, S waves, Rayleigh waves, and Love waves.
◦ P waves (primary waves) are the fastest seismic waves and travel through both solids and liquids. They cause particles to move in a compressional motion, similar to a slinky.
‣ P Waves (Primary Waves)
‣ Where They Occur: They travel through the Earth’s interior, passing through both solids and liquids.
‣ How They Move: They cause particles to move in a compressional motion, like a slinky being pushed and pulled. Think of it like a sound wave traveling through air, where particles move back and forth in the direction of the wave's movement.
‣ Speed: P waves are the fastest seismic waves and are the first to be detected by seismographs.
◦ S waves (secondary waves) are slower than P waves and only travel through solids. They cause particles to move perpendicular to the direction of wave travel, like a wave in a rope.
‣ Where They Occur: These also travel through Earth’s interior, but they can only move through solids (not liquids).
‣ How They Move: They cause particles to move perpendicular to the direction the wave is traveling, like a wave in a rope moving up and down. Imagine shaking a rope up and down — the movement is vertical while the wave moves horizontally.
‣ Speed: S waves are slower than P waves and arrive second.
◦ Rayleigh waves are surface waves that cause vertical, rolling motions similar to ocean waves and are slower than body waves.
‣ Where They Occur: These are surface waves, meaning they travel along the Earth’s surface.
‣ How They Move: Rayleigh waves cause vertical, rolling motions similar to ocean waves. The ground moves up and down, and the motion is often compared to a boat moving in the water.
‣ Speed: They are slower than both P and S waves.
◦ Love waves, another type of surface wave, move side-to-side, causing horizontal shaking.
‣ Where They Occur: Love waves also travel along the Earth’s surface, like Rayleigh waves.
‣ How They Move: They cause side-to-side shaking of the ground, moving horizontally. Imagine a rope being shaken left and right — that’s how Love waves move the ground.
‣ Speed: Love waves are also slower than P and S waves, and they travel faster than Rayleigh waves.
◦ Surface waves (Rayleigh and Love waves) typically cause the most damage during an earthquake due to their slower movement but larger amplitude. P waves and S waves are body waves, traveling through Earth's interior, with P waves arriving first and S waves following.
• What scale represents earthquake magnitude (what is it based on and what is the maximum level on this scale)?
◦ The Moment Magnitude Scale (MMS) is called so because it measures the seismic moment of an earthquake, which is a more accurate way to quantify the size of an earthquake compared to older scales like the Richter scale. The term "moment" in the name refers to seismic moment, which is a measure of the total energy released by an earthquake.
◦ The scale that represents earthquake magnitude is the Moment Magnitude Scale (formerly the Richter scale). This scale is based on the amplitude of seismic waves recorded by a seismograph and the amount of energy released by the earthquake. It is logarithmic, meaning each whole number increase on the scale represents a tenfold increase in ground motion and approximately 32 times more energy release. The maximum level on this scale is not defined, but the largest recorded earthquake was a magnitude 9.5, which occurred in Chile in 1960.
‣ The Moment Magnitude Scale is based on:
‣ The amplitude of seismic waves recorded by a seismograph.
‣ The amount of energy released during the earthquake.
‣ The scale is logarithmic, meaning that each increase of one unit on the scale represents a tenfold increase in the amplitude of seismic waves and about 32 times more energy release.
• What scale represents earthquake intensity (what is it based on and how many categories are there)?
◦ The Modified Mercalli Intensity Scale is called "modified" because it is an updated version of the original Mercalli Intensity Scale. based on people's subjective experiences of the earthquake, such as how much shaking they felt and the damage it caused. The "Modified" part refers to changes made in the 20th century to improve the scale's reliability and objectivity.
◦ The scale that represents earthquake intensity is the Modified Mercalli Scale. It is based on the effects of the earthquake on people, buildings, and the Earth's surface. There are 12 categories on the scale, ranging from I (not felt) to XII (total destruction). The intensity is measured using Roman numerals and varies depending on factors like ground materials, population density, and distance from the epicenter.
◦ It measures earthquake intensity, not magnitude, meaning it focuses on how strong the earthquake feels and what kind of damage it causes, rather than how much energy was released at the source.
◦ Intensity is influenced by factors like distance from the epicenter, type of ground materials (e.g., soft vs. hard rock), population density, and building structures.
◦ The scale has 12 levels, each represented by Roman numerals, from I to XII.
◦ I means the earthquake is not felt by people.
◦ V means it’s felt by most people and may cause some damage to buildings.
◦ XII means total destruction, where everything is shaken apart and even the Earth’s surface is permanently altered.
• What 6 hazards are associated with earthquakes? Be able to briefly describe each.
◦ The six hazards associated with earthquakes are GALLET:
‣ Ground Shaking -- The vibrations caused by seismic waves can cause structures to collapse, with the severity depending on the earth materials.
• This is the most immediate and widely recognized effect of an earthquake. When seismic waves travel through the Earth, they cause the ground to shake. The intensity of the shaking depends on factors like the size of the earthquake, the distance from the epicenter, and the type of ground or rock the waves travel through. The shaking can cause buildings and infrastructure to collapse, leading to significant damage, injuries, and fatalities.
‣ Aftershocks – Smaller earthquakes that follow the main event, part of the process of fault adjustment, can cause further damage.
• Aftershocks are smaller earthquakes that occur after the main earthquake event. They happen because the Earth's crust is adjusting to the stress released during the main quake. Aftershocks can be just as dangerous as the main quake, particularly if the initial damage has weakened structures, making them more susceptible to collapse. They can occur days, weeks, or even months after the primary earthquake.
‣ Landslides – Shaking on steep slopes can trigger landslides, leading to destruction and fatalities.
• The shaking of the ground can destabilize steep slopes, causing landslides or rockfalls. These landslides can bury roads, buildings, and even people, causing significant destruction, especially in mountainous areas. Areas with loose soil or steep terrain are especially vulnerable to landslides during an earthquake. Landslides can also block rivers, leading to flooding.
‣ Elevation Changes – Earthquakes can cause shifts in land elevation, such as raising or lowering mountains.
• Earthquakes can cause the land's surface to shift, either raising or lowering it. These shifts can affect roads, bridges, and buildings, rendering them unstable or unusable. For example, an earthquake might cause a mountain to rise, or a valley to sink. These changes can affect local ecosystems and waterways, sometimes even causing flooding or altering the course of rivers.
‣ Liquefaction – In areas with water-saturated soil, the shaking can cause the ground to behave like a liquid, leading to buildings sinking.
• In areas with loose, water-saturated soil (like wetlands or coastal regions), the shaking from an earthquake can cause the ground to temporarily lose its solidity and behave like a liquid. This phenomenon is known as liquefaction. During liquefaction, buildings and structures can sink or tilt as the ground beneath them becomes unstable. It's a major risk in areas with sandy or silty soils that are near water bodies.
‣ Tsunami – Underwater earthquakes can trigger large ocean waves, causing widespread flooding and destruction along coastlines.
• Underwater earthquakes, particularly those occurring at subduction zones (where one tectonic plate is forced beneath another), can displace large amounts of water. This displacement creates massive waves that spread outward across the ocean, known as tsunamis. When these waves reach coastlines, they can cause widespread flooding and destruction. Tsunamis can cause damage far beyond the earthquake's epicenter, as the waves can travel across entire ocean basins.
•
• What locations on Earth generally have the largest and most deadly earthquakes?
◦ The largest and most deadly earthquakes generally occur along convergent plate boundaries, where two tectonic plates collide, particularly at oceanic trenches.
◦ they happen there because:
‣ Subduction zones: In some places, one plate is forced under another (this is called subduction). As the plate sinks, it creates stress in the Earth's crust, leading to earthquakes.
‣ Oceanic trenches: These are deep areas in the ocean where two plates meet and one is subducted beneath the other. Earthquakes that happen here can be very powerful.
◦ The most significant earthquakes are often associated with subduction zones, such as in Indonesia, Chile, and Japan.
‣ Indonesia: Located near the Indo-Australian plate and the Eurasian plate, where there are many subduction zones.
‣ Chile: Along the Nazca plate and the South American plate, where subduction creates powerful quakes.
‣ Japan: The Pacific plate is subducting beneath the North American plate, leading to large earthquakes in the region.
◦ In the United States, the largest earthquakes occur south of Alaska along a convergent plate boundary.
‣ South of Alaska: This area has the largest earthquakes in the U.S. because of the collision of the Pacific plate and the North American plate.
◦ What makes these earthquakes so deadly?
‣ Populated areas: Earthquakes near densely populated regions, like California, cause significant damage. Even though California has earthquakes often, the bigger ones can lead to mass destruction.
‣ Seismic gaps: These are parts of active faults that have not had recent earthquakes. They build up stress and could cause big earthquakes in the future. Areas with seismic gaps are often areas to watch for the next major earthquake.
• What should you do during an earthquake?
◦ During an earthquake, it’s important to stay calm and act quickly. If you’re indoors, drop to the ground, take cover under a sturdy piece of furniture like a table or desk, and hold on until the shaking stops. Stay away from windows, doors, and anything that could fall or shatter. If you’re outside, move to an open area away from buildings, trees, and power lines. If you’re in a car, pull over to a safe location and remain inside the vehicle until the shaking stops. After the shaking ends, be prepared for aftershocks and check for hazards like gas leaks or electrical issues.
◦ drop cover hold on
Lecture: Tsunami
• Know the definitions for the components of a wave and its characteristics
◦ Basic Wave Components
‣ Crest – The highest point of the wave.
‣ Trough – The lowest point of the wave.
‣ Wave Height (H) – The vertical distance from the trough to the crest.
‣ Wavelength (L) – The horizontal distance between two successive crests or troughs.
‣ Wave Steepness (H/L) – The ratio of wave height to wavelength. If it exceeds 1/7, the wave breaks.
◦ Wave Movement and Behavior
‣ Wave Period (T) – The time it takes for one full wavelength to pass a fixed point.
‣ Wave Frequency (f) – How many waves pass a point in a given time (measured as 1/T).
‣ Orbital Motion – The movement of water particles in circular paths as a wave passes.
‣ Deep-Water Waves – The orbital motion decreases with depth and doesn’t reach the ocean floor.
‣ Shallow-Water Waves – The wave "feels" the bottom, causing the orbits to flatten and the wave to slow down.
◦ A wave is a disturbance that transfers energy through a medium, such as water. Waves have several components: the crest (highest part), the trough (lowest part), wave height (vertical distance between crest and trough), and wavelength (horizontal distance between two corresponding parts of successive waves). The wave steepness is the ratio of wave height to wavelength (H/L), and if steepness is greater than 1/7, the wave breaks. Wave period (T) is the time it takes for one wavelength to pass a fixed point, and wave frequency (f) is the inverse of the period (1/T). Waves transmit energy through the cyclic motion of particles, which move in orbital paths in ocean waves. In deep water, the diameter of orbital motion decreases with depth, and particles move in circular paths. In shallow water, waves feel the bottom and flatten.
‣ Tsunamis are seismic sea waves caused by sudden sea floor changes, usually from earthquakes. Tsunami waves have long wavelengths (over 100 km), move fast in deep water (up to 760 km/h), and slow down as they approach shore, causing wave height to increase. The first sign of a tsunami is usually a rapid change in sea level, with a rise followed by a sharp fall. Tsunamis can cause significant damage, and their warning systems use seismic wave recordings and buoys to detect them.
• Be able to distinguish between deep-water and shallow-water waves if given information about wavelength and water depth. Know what controls the speed of each type of wave. *you don’t need to memorize the equations
◦ Deep-water waves occur when the water depth is greater than half the wavelength (L/2).
‣ The water depth is greater than half of the wave’s wavelength (Depth > L/2).
‣ Example: If a wave has a wavelength of 100 meters, the water must be deeper than 50 meters for it to be a deep-water wave.
◦ Their speed depends on wavelength: longer waves travel faster.
‣ A long-stride runner (long wavelength) covers more ground per step and moves faster.
‣ A short-stride runner (short wavelength) takes many small steps and moves slower.
◦ Shallow-water waves occur when the water depth is less than 1/20 of the wavelength (L/20).
‣ ex: wavelength 100m, water depth 5m
• As waves move into shallower water, the bottom of the wave drags along the ocean floor, causing it to slow down.
• Deeper Water = Faster Speed – In deeper areas, there is less friction with the seafloor, so waves can move faster.
• Shallower Water = Slower Speed – In very shallow areas, waves slow down dramatically, causing them to build up in height (like tsunamis near shore).
◦ Their speed depends only on water depth: deeper water means faster waves. Tsunamis are shallow-water waves because their wavelength is much longer than the ocean depth. In deep water, tsunami waves move quickly with low height, but as they approach shore, their speed decreases, and wave height increases dramatically.
• How is a tsunami formed?
◦ How is a tsunami formed?
‣ vertical displacement of the sea floor and of water
‣ A tsunami happens when a large amount of water is suddenly displaced:
‣ Earthquakes – Most common cause! If an underwater earthquake moves the seafloor up or down, it pushes a huge amount of water, creating waves.
‣ Landslides – If part of a coastline or underwater slope collapses, it can displace water and generate a tsunami.
‣ Volcanic Eruptions – Explosive eruptions or collapsing volcanoes (like a caldera collapse) can push large amounts of water.
‣ Meteorite Impacts – A large space rock hitting the ocean would cause a massive displacement and trigger a tsunami.
• What is a typical wavelength and period for a tsunami?
◦ Unlike wind-driven waves (which only disturb the surface), a tsunami moves the entire column of water, from the seafloor to the surface.
◦ Since this displacement happens over a huge area, the energy is distributed over a much longer distance rather than forming short, choppy waves.
◦ In physics, energy prefers to spread in the most stable and efficient way possible.
◦ Instead of forming many short waves (which would lose energy quickly), the ocean naturally forms a single, long, low wave that carries energy efficiently across vast distances.
◦ This leads to the formation of a wave with an extremely long wavelength—often 100 km (60 miles) or more!
‣ A tsunami is different—it disturbs the entire ocean depth, so it must distribute its energy across a much greater horizontal distance.
◦ In deep water, tsunamis move very fast—up to 760 km/hr (470 mph) (as fast as a jet plane! ✈).
◦ But because the wavelength is so long, the wave height is usually very small in the open ocean, making it hard to detect.
◦ As the tsunami reaches shallow water, its speed slows down, and the wave height builds up dramatically.
◦ This is why a tsunami can appear as a rapid rise in sea level, followed by massive, destructive waves.
◦ The period of a tsunami (time between wave crests) is much longer than normal waves: 10 to 60 minutes per wave.
◦ A tsunami is formed when a sudden disturbance, such as an earthquake, underwater landslide, volcanic eruption, or meteorite impact, causes a vertical displacement of the seafloor. This displaces the water above, creating waves that spread outward in all directions. In the open ocean, tsunami waves have long wavelengths, typically greater than 100 km (60 miles), and travel at very high speeds, up to 760 km/hr (about 470 mph). However, their wave height is low, making them difficult to detect. As they approach the shore, their speed decreases due to the shallower water, but their height increases dramatically, leading to powerful and destructive waves. The typical period of a tsunami (the time it takes for one full wave cycle to pass a fixed point) ranges from 10 to 60 minutes.
• What happens when a tsunami is in deep water? How does this change when it approaches a coastline?
◦ When a tsunami is in deep water, it travels extremely fast, often over 700 km/hr, but has a very low wave height, making it almost undetectable. As it approaches a coastline and the water becomes shallower, the wave slows down due to friction with the ocean floor. This causes the wave height to increase dramatically, sometimes reaching over 30 meters, leading to massive destruction when it reaches land. The first sign of an approaching tsunami is often a rapid change in sea level, either a sudden rise or a sharp retreat of water, followed by powerful waves that can continue for hours.
• What are swash and backwash? How does water impact coastal areas during a tsunami event?
‣ Swash → The forward motion of water rushing up the shore after a wave breaks. It carries sand and debris onto the beach
• Massive Swash
◦ Tsunami waves don’t just break like normal waves—they surge far inland, pushing huge volumes of water, sediment, and debris with them.
◦ This can flood buildings, uproot trees, and destroy infrastructure..
‣ Backwash → The water returning back to the ocean after swash. It pulls sediment and objects back into the sea.
• Destructive Backwash
◦ When the water rushes back to the ocean, it carries debris, sand, and even entire buildings with it.
◦ People and objects caught in the backwash can be dragged out to sea.
• The force of a tsunami can completely reshape coastlines, washing away beaches and carving out new channels.
• Tsunami waves mix sediment into the water, turning it brown as they stir up sand, soil, and debris.
• warning sign: A sudden retreat of water from the shoreline (extreme backwash before the main wave arrives).
• Tsunamis drastically reshape coastlines through erosion and sediment transport.
◦ Swash is the movement of water rushing up the shore after a wave breaks, while backwash is the water flowing back into the ocean. During a tsunami, swash and backwash are much more powerful than in regular waves, leading to massive coastal erosion and destruction. As the tsunami waves reach the coast, they transport large amounts of sediment and debris inland with the swash. When the water recedes with the backwash, it can drag buildings, vehicles, and even people back into the ocean. The transformation stage of tsunami waves incorporates sediment into the water, turning it brown near the shore. The first sign of an approaching tsunami is often a rapid change in sea level, either a sudden retreat or a rising wall of water.
• How does the DART observation & PTWC warning system work? How has this changed since 2004?
◦ the DART (Deep-ocean Assessment and Reporting of Tsunamis)
‣ What it is: A network of buoys and seabed pressure sensors that detect tsunami waves in the deep ocean.
‣ Seabed pressure sensors detect small changes in water pressure, indicating a passing tsunami wave.
‣ The sensors send this data to a surface buoy, which then relays it via satellite to tsunami warning centers.
‣ Scientists analyze the data in real-time to confirm if a tsunami is forming and estimate its size and arrival time.
◦ system consists of buoys and seabed pressure sensors that detect tsunami waves in the deep ocean. When an undersea earthquake occurs, these sensors measure pressure changes in the water column and send real-time data to the Pacific Tsunami Warning Center (PTWC) via satellite.
◦ The PTWC analyzes this data along with seismic readings to determine if a tsunami threat exists.
‣ Pacific Tsunami Warning Center (PTWC)
‣ What it does: Uses data from DART buoys, seismic sensors, and computer models to predict tsunami behavior.
‣ How it issues warnings:
‣ When an earthquake occurs, PTWC analyzes seismic activity to determine if a tsunami is possible.
‣ If a tsunami is detected, warnings are issued to at-risk coastal regions.
‣ Alerts go out through radio, television, text messages, sirens, and emergency systems.
◦ Since 2004, the DART system has expanded from six to over 60 stations worldwide, improving detection accuracy and response times. Advances in technology have also enhanced modeling capabilities, allowing for more precise forecasts and faster warnings to at-risk coastal communities.
• What are the differences between the 4 categories of tsunami alerts? WAWI
◦ Tsunami Warning 🚨 (Highest Alert)
◦
◦ What it means: A tsunami is occurring or expected to cause major impacts.
◦ What to do: Immediate evacuation to higher ground or inland is necessary. Stay away from the coast.
◦ Issued when: A tsunami has been confirmed by DART buoys, tide gauges, or visible waves.
◦ Example impact: Large, destructive waves that flood coastal areas.
◦ Tsunami Advisory ⚠ (Moderate Alert)
◦
◦ What it means: A tsunami is expected to cause strong currents and dangerous waves, but not major flooding.
◦ What to do: Avoid beaches, harbors, and marinas. Boats should move to deeper water if possible.
◦ Issued when: A tsunami is detected, but wave heights are not expected to cause severe damage.
◦ Example impact: Strong surges in harbors, dangerous rip currents, and minor coastal flooding.
◦ Tsunami Watch 👀 (Be Prepared)
◦
◦ What it means: A large earthquake has occurred, and a tsunami may be generated.
◦ What to do: Stay alert for updates and be ready to evacuate if upgraded to a warning.
◦ Issued when: A tsunami has not yet been confirmed, but conditions suggest one is possible.
◦ Example impact: No immediate effects, but monitor news and warnings closely.
◦ Tsunami Information Statement ℹ (No Threat)
◦
◦ What it means: An earthquake has occurred, but it does not pose a tsunami threat.
◦ What to do: No action needed, but it provides information for awareness.
◦ Issued when: Either the earthquake is too small or located in a way that won’t generate a tsunami.
◦ Example impact: None—just an update for public and scientific monitoring.
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Lecture: Volcanoes
• Know the differences between erupting, dormant, and extinct volcanoes
◦ An erupting volcano is an active volcano that is currently having an eruption. A dormant volcano is an active volcano that is not erupting but is expected to erupt again. Volcanoes can be active over millions of years, with long periods of inactivity between eruptions, sometimes luring people to live nearby due to fertile volcanic soil. An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable future timescale.
• Be able to explain how volcanoes form related to plate tectonics
◦ Divergent Boundaries (Spreading Centers) 🌍⬅➡
‣ How? Plates move apart, allowing magma to rise and solidify, forming new crust.
‣ Where? Mid-ocean ridges (e.g., Mid-Atlantic Ridge), rift valleys.
‣ Example? Iceland (formed by volcanic activity at a divergent boundary).
◦ Convergent Boundaries (Subduction Zones) 🌍➡⬅
‣ How? One plate sinks beneath another into the mantle, melting and generating magma.
‣ Where? Pacific "Ring of Fire" (oceanic-continental subduction zones).
‣ Example? Andes Mountains (South America), Japan’s volcanoes.
◦ Hotspots (Not at Plate Boundaries) 🔥
• How? Magma rises from deep mantle plumes, forming volcanoes away from plate boundaries.
◦ Where? Middle of tectonic plates.
‣ Example? Hawaiian Islands (volcanic chain formed as the Pacific Plate moved over a stationary hotspot).
◦ Volcanoes form due to processes related to plate tectonics. About 90% of volcanic activity is associated with plate boundaries, with 80% occurring at spreading centers (divergent boundaries) and around 10% at subduction zones (convergent boundaries). At divergent boundaries, magma rises from the mantle as tectonic plates move apart, creating new crust and forming volcanoes, often underwater. At convergent boundaries, one plate is forced under another (subduction), leading to melting of the subducted plate and the formation of volcanoes on the overriding plate. The remaining 10% of volcanism occurs at hotspots, where plumes of magma rise from deep in the mantle, forming volcanic islands like the Hawaiian Islands.
• What is a hotspot and what % of volcanoes form from them? What about the % at other plate boundaries?
◦ Think of a blowtorch under a moving conveyor belt. The torch (hotspot) stays in place, but the belt (tectonic plate) moves, creating a chain of volcanoes over time.
◦ Hotspots are areas where a plume of magma rises from deep in the mantle, creating volcanic activity away from plate boundaries. Around 10% of volcanoes form from hotspots. The remaining 90% of volcanism is associated with plate boundaries: 80% at spreading centers (divergent boundaries) and about 10% at subduction zones (convergent boundaries).
• Know the difference between magma and lava
◦ Magma is molten rock beneath the Earth's surface, while lava is molten rock that has reached the surface through a volcanic eruption. lava lips (open mouth) molten closes (mouth starts closed)
• What makes a volcano erupt?
‣ magma rises due to heat and pressure. As it moves up, pressure drops, allowing gas bubbles to expand, which pushes the magma to the surface.
‣ Low-viscosity magma (runny) → Gases escape easily → Gentle eruptions (e.g., Hawaii).
‣ High-viscosity magma (thick) → Traps gases → Explosive eruptions (e.g., Mount St. Helens).
‣ The deeper the magma is, the more pressure it experiences from the weight of the overlying rock. As the magma moves upward, the amount of rock pressing down on it decreases, leading to a drop in pressure.
• As magma rises toward the Earth's surface, the pressure decreases. When pressure drops, the magma can start to melt or expand, causing it to push upwards and potentially erupt.
‣ Raising Temperature: If the temperature of the magma increases (for example, by nearby hot areas or deeper mantle heat), the rock surrounding it can melt more easily, creating more magma that may lead to an eruption.
‣ Adding Water: Water can mix with hot rock, lowering its melting point. This makes it easier for the rock to melt and form magma, which can lead to an eruption.
• When water interacts with hot rock, it chemically weakens the bonds between minerals in the rock. This allows the rock to melt at a lower temperature than it normally would.
◦ A volcano erupts when magma beneath the Earth's surface rises due to heat and pressure. As magma moves upward, the pressure decreases, allowing gases dissolved in it to form bubbles. These expanding gas bubbles push the magma to the surface, sometimes causing explosive eruptions. The type of eruption depends on the magma's viscosity, which is influenced by temperature and composition. Lower viscosity magma allows gases to escape easily, leading to milder eruptions. Higher viscosity magma traps gases, resulting in more explosive eruptions. Factors like lowering pressure, raising temperature, or adding water can melt rock and form magma, causing eruptions.
• Know the 3 main types of magma: know where each is formed and be able to compare their silica content and how this affects their viscosity/ intensity of eruption (as well as how this relates to the different plate boundaries) BAR
◦ Basaltic Magma: (basaltic = basalt rock... base, pull apart = low), shield volcano
‣ Silica Content: Low (about 45-55% silica).
‣ Where It Forms: Mostly at divergent boundaries (like mid-ocean ridges) and hotspots. ocean low and hotspots low %
• forms here bv of the melting trockmhere low in silica
‣ Viscosity: Low viscosity, which means it flows easily.
‣ Eruption Style: Mild eruptions. The low viscosity allows gases to escape easily, resulting in non-explosive lava flows.
‣ Example: Hawaiian volcanoes (shield volcanoes)
◦ Andesitic Magma: (andesite rock... and middle, come together, and = bridge, convergent, subduction zones) stratovolcano
‣ Silica Content: Intermediate (about 55-65% silica).
‣ Where It Forms: Typically at convergent plate boundaries (subduction zones).
• When an oceanic plate subducts beneath a continental plate, the subducted oceanic crust melts as it descends into the mantle due to increased temperature and pressure. However, water trapped in the oceanic crust lowers the melting point of the surrounding rock, causing partial melting.
• This partial melting creates magma that is intermediate in composition, containing more silica than basaltic magma but less than rhyolitic magma. This is because some of the continental crust also melts into the magma, adding silica.
‣ Viscosity: Medium viscosity, meaning it is thicker than basaltic magma but not as thick as rhyolitic magma.
‣ Eruption Style: Moderate eruptions. The medium viscosity causes some trapping of gases, leading to more explosive eruptions than basaltic lava but less than rhyolitic lava.
‣ Example: Stratovolcanoes like Mount St. Helens.
◦ Rhyolitic Magma: (rhyolite, rise = high) stratovolcano
‣ Silica Content: High (about 65-75% silica).
‣ Where It Forms: Typically from partial melting of continental crust, often associated with continental volcanic arcs.
• Continental crust is made of rock that is rich in silica. When part of the continental crust melts due to heat from the mantle (e.g., from subduction or a hotspot), the resulting magma is rhyolitic, as the continental crust has high silica content.
‣ Viscosity: High viscosity, meaning it is very thick and resistant to flow.
‣ Eruption Style: Explosive eruptions. The high viscosity traps gases, causing pressure to build up until it results in violent eruptions.
‣ Example: Yellowstone, which has supervolcanoes.
• What are the 3 main types of volcanoes, including what they look like and what types of magma make up each
◦ Shield Volcanoes:
‣ Appearance: Shield volcanoes have broad, gentle slopes that resemble a warrior's shield.
‣ Magma Type: They are primarily made up of basaltic magma, which has low viscosity.
‣ Eruptions: The low-viscosity magma allows lava to flow easily, leading to relatively mild eruptions. These volcanoes typically form at hotspots or divergent plate boundaries, such as the Hawaiian Islands.
◦ Stratovolcanoes (Composite Volcanoes):
‣ Appearance: Stratovolcanoes have steeper, more conical slopes.
‣ Magma Type: These volcanoes are formed from a combination of medium to high-viscosity lava, like andesitic and rhyolitic magma, and tephra (volcanic ash, rocks, and debris).
‣ Eruptions: Eruptions tend to be more explosive and violent because the magma is more viscous, causing pressure to build up inside the volcano. Stratovolcanoes are commonly found at convergent plate boundaries, such as Mount Fuji in Japan or Mount St. Helens in the U.S.
◦ Cinder Cone Volcanoes:
‣ Appearance: Cinder cone volcanoes are the smallest type, with steep, conical slopes.
‣ Magma Type: These volcanoes are made from more viscous magma, producing tephra (pieces of volcanic rock) that accumulate around a single vent.
‣ Eruptions: The eruptions are typically short-lived but can be quite explosive, resulting in the formation of coarse, fragmented tephra. Cinder cone volcanoes can be found on the flanks of larger volcanoes or as standalone features.
◦ The three main types of volcanoes are shield, stratovolcanoes (also known as composite volcanoes), and cinder cone volcanoes. Shield volcanoes have broad, gentle slopes and are built from many low-viscosity lava flows, mainly basaltic magma, which leads to mild eruptions. These volcanoes are commonly found at hotspots or divergent plate boundaries, like the Hawaiian Islands. Stratovolcanoes have steeper slopes and are formed from alternating layers of tephra and medium to high-viscosity lava, such as andesitic and rhyolitic magma. They are typically found at convergent plate boundaries, such as Mount Fuji in Japan. Cinder cone volcanoes are the smallest type, with steep slopes, and are made from particles and blobs of congealed lava ejected from a single vent. They are built from more viscous magma, producing coarse tephra, and may form on the slopes of shield or stratovolcanoes.
‣ When this viscous magma is expelled from the volcano, it cools quickly in the air and solidifies into small fragments, called tephra, which can include ash, cinders, and small rocks. These solidified fragments pile up around the volcano's vent, forming the steep cone shape.
• Know the scale for classifying a volcanic eruption (name and # of categories)
◦ volcanic explosivity index vei, 9 categroies (0-8)
◦ The scale for classifying volcanic eruptions is the Volcanic Explosivity Index (VEI), which has 9 categories. It measures the volume of erupted material, with each category representing an increase in the eruption's intensity and volume. The categories range from 0 (non-explosive) to 8 (extremely explosive). The higher the number, the more significant the eruption in terms of material volume and explosiveness.
‣ A pyroclastic flow is a fast-moving, extremely hot mixture of gas, ash, and volcanic rock fragments that is ejected from a volcano during an explosive eruption. These flows are typically made up of gases such as water vapor, carbon dioxide, and sulfur dioxide, along with hot ash and fragments of volcanic rock.
• Be able to describe the major products of volcanic eruptions, and to identify which are airborne and which are land-based
• Airborne Products:
◦ Volcanic Gases:
‣ These include water vapor (H2O), sulfur dioxide (SO2), and carbon dioxide (CO2).
‣ Water vapor can contribute to rainfall and cloud formation.
‣ Sulfur dioxide can combine with water vapor in the atmosphere to form sulfuric acid, leading to acid rain. It can also cause temporary cooling of the Earth's atmosphere.
‣ Carbon dioxide is a greenhouse gas, though its atmospheric impact is generally smaller during volcanic eruptions compared to human activity.
◦ Tephra:
‣ These are solid particles that are ejected during volcanic eruptions.
‣ Ash: Fine particles that can travel long distances, disrupting air travel and damaging property and vegetation.
‣ Lapilli: Small volcanic stones.
‣ Lava Bombs: Large, solidified chunks of lava that can be ejected during explosive eruptions.
‣ Tephra can be carried by the wind and fall over large areas, causing damage to structures and reducing air quality.
◦ Lateral Blasts:
‣ Lateral (sideways) explosions can occur when magma, gas, or pressure escapes laterally from the volcano.
‣ These blasts can destroy everything in their path (including buildings, trees, and vegetation) up to 25 km away from the eruption point.
• Land-based Products:
◦ Lava:
‣ Lava is molten rock that flows down the slopes of a volcano.
‣ Viscosity determines how far the lava will travel. Low-viscosity lava (like basalt) flows easily and covers long distances, while high-viscosity lava (like andesite or rhyolite) flows more slowly.
‣ Lava flows can destroy buildings, roads, and landscapes.
◦ Pyroclastic Flows:
‣ These are hot, fast-moving mixtures of volcanic gases, ash, and rock fragments.
‣ They flow down the sides of a volcano and are very dangerous due to their speed (up to 700 km/h) and high temperature (up to 1,000°C).
‣ Pyroclastic flows can cause massive destruction to anything in their path.
◦ Lahars:
‣ Mudflows or volcanic debris flows formed when volcanic ash and debris mix with water from rain, rivers, or melted ice or snow.
‣ Lahars can travel long distances and cause flooding, damaging infrastructure and burying villages or towns.
◦ Landslides/Debris Avalanches:
‣ These are mass movements of rock and debris that occur when a volcanic eruption destabilizes the volcano's slopes.
‣ Landslides can bury areas near the volcano in debris, sometimes triggering lahars or blocking rivers, leading to flooding.
◦ The major products of volcanic eruptions can be categorized into airborne and land-based types. Airborne products include volcanic gases (such as water vapor, sulfur dioxide, and carbon dioxide) which can affect climate patterns, potentially causing temporary cooling or acid rain. Lateral blasts, or sideways explosions, can destroy buildings and trees up to 25 km away. Tephra refers to particles ejected during an eruption, ranging from fine volcanic ash to solidified lava bombs. These particles can be carried long distances by the wind. Land-based products include lava, which can flow over long distances depending on its viscosity, pyroclastic flows—dense, hot clouds of tephra and gases that race down volcanic slopes, lahars—mudflows formed when volcanic debris mixes with streams or melting ice, and landslides or debris avalanches triggered by volcanic activity.
• What are some signs that an eruption might happen soon?
◦ Some signs that an eruption might happen soon include: 1. Gas leaks: release of gases like H2O, CO2, and SO2 from magma into the atmosphere through cracks in the rock. 2. Bit of a bulge: deformation of part of the volcano, indicating that the magma chamber at depth is swelling or becoming more pressurized. 3. Getting shaky: small earthquakes, which indicate magma is moving and forcing surrounding rocks to crack. 4. Dropping fast: a sudden decrease in seismicity, which may suggest magma has stalled. 5. Big bump: a pronounced bulge on the side of the volcano, signaling magma moving close to the surface. 6. Blowing off steam: steam eruptions when magma heats groundwater to the boiling point, causing explosions that send rock fragments into the air.
• What should you do during an eruption? Where is risk highest in the U.S. (FEMA)
◦ During a volcanic eruption, stay indoors away from ash fall, follow evacuation orders, and avoid low-lying areas prone to lava flows, pyroclastic flows, or lahars. Wear protective clothing, cover your nose and mouth with a cloth or mask, and stay in a safe location. In the U.S., the highest risk for volcanic eruptions is in the Pacific Northwest (e.g., Mount St. Helens), Hawaii, and Alaska. FEMA recommends preparedness by having an emergency kit, an evacuation plan, and staying informed through alerts.
◦ During a volcanic eruption, here are the recommended actions to take:
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◦ ### What to do during a volcanic eruption:
◦ 1. Stay indoors: Stay inside to avoid ash fall and other airborne hazards.
◦ 2. Follow evacuation orders: If local authorities issue evacuation orders, follow them immediately.
◦ 3. Avoid low-lying areas: Stay away from areas that are at risk of lava flows, pyroclastic flows, or lahars (volcanic mudflows).
◦ 4. Wear protective clothing: Wear long sleeves, pants, and goggles to protect yourself from ash and debris.
◦ 5. Cover nose and mouth: Use a cloth, mask, or damp cloth to cover your nose and mouth to avoid inhaling ash or toxic gases.
◦ 6. Stay in a safe location: Stay in a location that offers protection from ash and pyroclastic materials, such as an enclosed building or designated evacuation shelter.
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◦ ### If you are near or downwind of a volcano:
◦ 1. Stay off fresh lava flows: Avoid walking on fresh lava flows, as they are extremely dangerous and can emit toxic gases.
◦ 2. Burning vegetation: Be cautious of areas where burning vegetation may release methane gas that could accumulate and cause explosions.
◦ 3. Lahars: If authorities issue a warning of an approaching lahar, seek high ground as quickly as possible and find shelter away from the path.
◦ 4. Seal doors and windows: Close and seal doors, windows, vents, and other gaps in your home. Use damp towels at the bottom of external doors to minimize ash and gas infiltration.
◦ 5. Minimize HVAC use: Avoid using HVAC or heating/cooling systems that draw outside air into the building.
◦ 6. Evacuate if necessary: If you're ordered to evacuate, do so immediately and take your emergency kit and important documents with you.
◦ 7. Avoid driving: Driving in ashfall is hazardous as ash can damage your vehicle's engine, filters, and body. If you must drive, drive slowly and carefully.
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◦ ### Where is the risk highest in the U.S.?
◦ The highest volcanic eruption risk in the U.S. is found in the following regions:
◦ 1. Pacific Northwest (e.g., Mount St. Helens in Washington State) – Due to subduction of the Juan de Fuca Plate beneath the North American Plate, this area is known for frequent volcanic activity, particularly in the Cascade Range.
◦ 2. Hawaii – Due to the presence of hotspot volcanoes like Kīlauea and Mauna Loa.
◦ 3. Alaska – Alaska has numerous active volcanoes, many of which erupt frequently.
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◦ FEMA recommends volcanic activity preparedness by:
◦ - Having an emergency kit ready with essentials (water, food, medical supplies).
◦ - Creating an evacuation plan that includes routes and meeting points.
◦ - Staying informed through emergency alerts and weather services that monitor volcanic activity.
Lecture: Mass Movements
• What are the 3 main types of weathering? How does each generally work (including their subtypes)?
◦ The three main types of weathering are physical, chemical, and biological weathering. Physical weathering involves the disintegration of rocks into smaller pieces due to mechanical forces, such as unloading (erosion strips overlying material, causing rock to expand) and wedging (water entering cracks, freezing, and expanding).
‣ Definition: The breakdown of rocks into smaller pieces without changing their chemical composition.
‣ Subtypes:
‣ Unloading: Erosion removes overlying material, reducing pressure and causing the underlying rock to expand and crack.
‣ Wedging: Water enters cracks, freezes, and expands, gradually forcing the cracks to widen. Repeated cycles lead to further fragmentation.
‣ Example: Potholes forming in roads due to freeze-thaw cycles.
◦ Chemical weathering occurs when minerals in rocks are chemically altered by reactions with water, like dissolution (minerals dissolve), hydrolysis (reaction with water), and oxidation (reaction with oxygen).
‣ Definition: The breakdown of rock due to chemical reactions that change the mineral composition.
‣ Subtypes:
‣ Dissolution: Water dissolves minerals (e.g., acid rain creating sinkholes).
‣ Hydrolysis: Water reacts with minerals, replacing ions and altering the rock’s structure.
‣ Oxidation: Oxygen reacts with minerals (e.g., iron forming rust).
‣ Factors influencing chemical weathering:
‣ Warmer, wetter climates accelerate reactions.
‣ Acidic water (more hydrogen ions) increases chemical breakdown.
‣ 3. Biological Weathering
◦ Biological weathering involves the breakdown of rocks by living organisms, such as plant roots or burrowing animals.
‣ Definition: The breakdown of rock by living organisms.
‣ Subtypes:
‣ Macroscopic: Visible organisms like plant roots, burrowing animals, and termites physically breaking rock apart.
‣ Microscopic: Microorganisms decompose materials, sometimes producing acids that contribute to chemical weathering.
‣ Example: Plant roots growing into cracks and widening them over time.
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• What are the main forces of erosion? How do the various factors control erosion rates?
◦ The main forces of erosion are water, wind, glaciers, and gravity.
◦ Water is the primary source, capable of moving most sizes of sediment, with faster water moving larger sediments.
‣ Water: The most powerful erosion force, capable of transporting sediments of various sizes. Faster-moving water carries larger sediments, while slower water deposits them.
◦ Wind moves sand-sized and smaller pieces, with higher wind speeds moving larger sediments.
‣ Moves sand-sized and smaller particles. Higher wind speeds transport larger sediments, while lower speeds move only fine materials.
◦ Glaciers can transport all sizes of sediment, from large boulders to tiny fragments.
‣ Carry a wide range of sediment sizes, from large boulders to fine particles, as they move slowly over land.
◦ Gravity moves sediment downslope, with steeper slopes increasing the impact of gravity.
‣ Drives mass movement (e.g., landslides, rockfalls), pulling sediments downslope. Steeper slopes accelerate this process. Erosion rates are controlled by several factors: climate (rainfall, wind velocity, and temperature), soil character (texture, structure, and permeability), vegetation cover (more cover reduces erosion), and land slope (steeper slopes increase erosion).
◦ factors:
‣ Climate: Higher rainfall increases water erosion, while strong winds enhance wind erosion. Temperature fluctuations contribute to weathering, making sediments more susceptible to erosion.
• more rain = more erosion water, more iwind = more wind erosion, temp contributes to weathering bc sediments r more susceptible with fluctuations
• Vegetation cover: Roots stabilize soil and reduce erosion by absorbing water and blocking wind. Areas with little vegetation experience higher erosion rates. roots stabilize soil by absorbing water and blocking wind
• soil characteristics:
◦ big grains are loosely packed and easily displaced
◦ smaller grains can be carried by water but they stick together
◦ clumpy strucutred soil resists erosion bc bound together
◦ loose sand or heaily compacted slay have less cohesion and clay due to surrface runofff
◦ sandy soils = high permeability so they can let water soak in which reduces runoff and erosion
◦ low permeability causes water to pool and run off os more erosion
• Slope gradient: Steeper slopes increase gravity-driven erosion and accelerate water runoff, leading to higher erosion rates.
• What forces control slope stability and how do they balance (or not) to create mass wasting?
‣ Slope stability is a battle between two main forces: gravity = SHEAR FORCE (which pulls materials downhill) and friction (SHEAR STRENGTH) (which holds them in place). When gravity overpowers friction, mass wasting—like landslides, rockfalls, or soil creep—happens.
• gravity = shear force, friction = shear strength
‣ Gravity pulls materials downward, creating a shear force parallel to the slope that can cause materials to move downslope. Friction, or shear strength, is the resistance that holds materials in place.
‣ When the shear force (gravity) exceeds the shear strength (friction), mass wasting (slope failure) occurs.
◦ What Influences Slope Stability?
‣ Slope Angle: Steeper slopes are more unstable. steeper slopes mean more fall
‣ Material Strength: Loose soil or fractured rock moves more easily than solid rock.
• loose weakly bound materials fall more
‣ Water: A little moisture can help particles stick together, but too much reduces friction and adds weight, making slides more likely.
• too much water reduces friction and adds weight
‣ Vegetation: Roots help hold soil in place, reducing erosion and slope failure.
‣ Earthquakes & Human Activity: Vibrations or construction can weaken slopes, triggering mass wasting.
• vibration and shaking and mvmt can loosen stuff
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‣ The balance between these forces is influenced by factors such as the angle of the slope, the strength of materials, and the presence of water. Water reduces friction, making materials weaker and more likely to slide. The steeper the slope and the weaker the material, the more likely mass wasting will occur. Additionally, the type of rock and the presence of fractures or water saturation play crucial roles in determining slope stability.
• How do rock type, fracture orientation, and water content impact the chance of mass wasting?
◦ Rock Type:
‣ Strong rocks like igneous (think granite) are less likely to slide because they’re tough and solid. igneous is tough and solid
‣ Weaker rocks like sedimentary (sandstone) or loose materials like soil are more likely to move because they break apart more easily. sedimentary
◦ Fracture orientation:
‣ If the cracks (fractures) are aligned with the slope (going in the same direction as the slope), the rock becomes weaker because the cracks act like natural breaks, making it easier for the rock to slide down the slope. It's like if you had a stack of bricks with cracks going horizontally – the bricks would be more likely to fall apart and slide down if the stack is tilted.
‣ If the cracks are at an angle or don't follow the slope (crossing the slope), the rock is stronger because the cracks don't line up with the direction of movement. The rock is more resistant to sliding because the cracks are less likely to let the pieces separate easily. Think of a stack of bricks with cracks going diagonally – it holds together better and is less likely to fall over.
◦ water content:
‣ Moist sediments are stronger because the water helps hold things together.
• water binds toghetehr in moist
‣ Dry sediments are weaker because the particles don’t stick together well.
• dry have no sticky
‣ Saturated sediments (when there’s too much water, like after heavy rain) are the weakest! The water pushes the particles apart, lowering friction, and making it easier for everything to slide downhill.
• too muhc water no cohesion and water pushes particles apart
◦ Rock type, fracture orientation, and water content significantly affect the likelihood of mass wasting. Rock type influences strength, with solid rocks like igneous being stronger than sedimentary or unconsolidated materials, which are weaker and more prone to movement. Fracture orientation plays a role in mass wasting by reducing the strength of rocks, especially when fractures are parallel to the slope, making the material more likely to slide. Water content impacts mass wasting by reducing friction between grains. Moist sediments are stronger due to surface tension, while dry sediments have weaker cohesion, and saturated sediments are the weakest as water pushes grains apart, reducing friction. An increase in water content, such as from heavy rain or rapid melting, can trigger slope failure by reducing shear strength and increasing the potential for mass wasting.
• What are the #1 and #2 triggers of mass wasting?
◦ Water content increase: When there’s a lot of water, it weakens the materials on a slope. This can happen from things like heavy rain, melting snow or ice, volcanic eruptions, or even human activities that change how water flows. More water makes the soil and rocks slippery, which can cause them to slide.
◦ Seismic shaking: Earthquakes or other ground shaking (like from nearby explosions) can suddenly loosen the material on a slope, causing it to move. The shaking disrupts the stability of the slope, triggering mass wasting.
◦ The #1 trigger of mass wasting is an increase in water content, which can result from rapid melting due to warming or volcanic eruptions, heavy rain, earthquake liquefaction, or human influence on runoff. The #2 trigger is seismic shaking, such as during an earthquake.
• What are the 3 categories of motion during a slope failure and their associated failure types? Which is fastest?
◦ Fall: This is when material, like rocks, drops almost straight down. It’s the fastest type of motion, happening at speeds of more than 10 meters per second. A rock fall is an example.
◦ Slide: Here, material moves along a sloped surface, like in a rock slide. This type happens more slowly, ranging from a few millimeters or centimeters per year to faster speeds depending on conditions.
◦ Flow: This is when material moves in a flowing motion, like in a mudflow or debris flow. The speed can vary, from moderate to fast (from centimeters per second to meters per second).
◦ The three categories of motion during a slope failure are: 1) Fall: Material drops vertically or nearly vertically, like a rock fall, and occurs at a very fast rate (greater than 10s of meters per second). 2) Slide: Material moves as a mass along a sloping surface, like a rock slide, and typically occurs at a slower rate (mm to cm per year, but can be faster). 3) Flow: Material moves with internal motion, like a mudflow or debris flow, and can vary from moderate to fast rates (cm per second to m/s). The fastest is a fall, specifically a rock fall.
• What are the two main types of avalanches? Which is most deadly? What are some common triggers for avalanches?
◦ Wet Avalanches: These happen when snow becomes heavy and slushy because it’s saturated with water. They move slower because of the wet snow, but they can still be dangerous.
‣ wet avalanches are sloggish and slushy
◦ Dry Avalanches: These occur when loose, dry snow slides down a slope. They are faster and can involve much more force, which is why dry avalanches are typically the most deadly.
‣ loose dry snow is more deadly and can involve more force
• loose and unstable can more more freely and quickly
• nto bound so less friction
• no extra weight from water
◦ triggers:
‣ Heavy snowfall: Adding more weight to the snowpack.
• heavy snowfall weighs it down more
‣ Rain on snow: Water makes the snow more likely to slide.
• rain makes it more slidey and breaks it down
• Rapid temperature changes: Sudden warming or cooling can destabilize the snow. quick temp change can destabilize the snow
‣ Human activity: Things like skiing or snowmobiling can trigger avalanches.
• skiing snow mobiles or other human producion can trigger break off
• earthquakes can dislodge or cause snow to slide
‣ Seismic shaking: Earthquakes can cause snow to slide down.
◦ The two main types of avalanches are wet avalanches and dry avalanches. Wet avalanches occur when snow becomes saturated with water, making it heavy and slushy, while dry avalanches happen when dry, loose snow slides down a slope. The most deadly type is typically dry avalanches because they travel faster and involve more force. Common triggers for avalanches include heavy snowfall, rain on snow, rapid temperature changes, and human activity, such as skiing or snowmobiling. Avalanches are also triggered by seismic shaking, like from earthquakes.
• Know the ways that human activity can increase the risk of mass movements
◦ Deforestation: Cutting down trees removes the roots that help hold soil together. Without this natural support, slopes become less stable and more prone to sliding.
‣ deforestation ruins the roots
◦ Urbanization and Construction: Building cities, roads, or structures can change the way water flows over the land, often increasing runoff. This extra water can weaken the soil and make slopes more vulnerable to movement.
‣ building development can change the way water flows over the land and can make slopes more vulnerable
◦ overgrazing by lize stock removes plants that keep soil in place so soil is exposed for landslides
◦ mining and excavation: diging into the ground for resources or construction = soil and rock disturbed = natural barriers weakened
◦ excess water added into the ground through irrigation, septic systems, or heavy rain = adds weight to slopes, less friction between soil particles
◦ Human activity can increase the risk of mass movements in several ways. Deforestation can reduce the stability of slopes by removing roots that help bind the soil. Urbanization and construction can alter natural drainage patterns, leading to increased water runoff that weakens slopes. Overgrazing by livestock can destabilize soil, while mining and excavation activities can disturb the ground, making it more susceptible to landslides. Additionally, the addition of excess water, such as from irrigation, septic systems, or heavy rainfall due to climate change, can increase the weight and decrease the cohesion of soil, triggering mass movements.
• What (if any) are the scales for landslide risk and avalanche risk in the U.S.?
◦ Landslide Risk:
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◦ Landslide Hazard Map (USGS): This map provides a general risk level based on factors like geology, slope, and rainfall.
◦ Landslide Susceptibility Map: This map assesses areas at risk for landslides, considering factors like soil and slope type.
◦ Landslide Frequency and Magnitude Models: These models help predict the likelihood and severity of landslides based on historical data and the types of landslides that have occurred in an area (e.g., rock, debris, or mudslides).
◦ Avalanche Risk:
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◦ Colorado Avalanche Information Center (CAIC) Avalanche Hazard Scale: This scale issues warnings ranging from Low to High based on snow conditions, weather, and terrain. The scale helps people assess the danger of avalanches in specific areas.
◦ Avalanche Risk Matrix: This tool evaluates the likelihood of an avalanche by considering factors like slope angle, snowpack stability, and weather conditions.
◦ In the U.S., landslide and avalanche risks are assessed using several scales. For landslides, the U.S. Geological Survey (USGS) uses the Landslide Hazard Map, which provides a general risk level based on factors like geology, slope, and rainfall. The Landslide Susceptibility Map and Landslide Frequency and Magnitude models help assess risk based on historical data and landslide types (e.g., rock, debris, or mudslides). For avalanches, the Colorado Avalanche Information Center (CAIC) and other regional centers issue Avalanche Hazard Scale warnings, ranging from Low to High based on snow conditions, weather, and terrain. The Avalanche Risk Matrix is also used, considering factors like slope angle and snowpack stability to predict avalanche likelihood.