Lecture 2-10: EPS 80 Midterm #2 FRQ

Lec 2 Q1: Describe what the lines of evidence are that demonstrate that many elements are made in stars, rather than all elements being present from the start of the universe.

Technetium was observed in stars even though its maximum half-life is only 4.2million years, showing it must have been produced. The abundance pattern of elements, including the Oddo-Harkins Rule and nucleosynthesis models, shows that stars and supernovae create heavier elements from hydrogen and helium.

Lec 2 Q2: Describe very approximately, the order of things that happened after our planet formed. Bullet points are fine, as are dates within 100 million years after 500 Ma, and ±500 Ma before 500 Ma

• Big Bang: a lot of the elements were synthesized 13.7 billion years ago

• Earth Formation: 4.6 Ga

• Moon formation: 4.4 Ga

• Light evolution: 4-3 Ga

• Rise of oxygen: 2-3 Ga

• 500 million year ago animal started to evolve

Lec 2 Q3: Describe the significance of banded iron formations in the context of oxygen evolution in Earth’s atmosphere.

Banded iron formations formed when oxygen produced by early photosynthetic organisms reacted with dissolved iron in the oceans. Their presence provides evidence that oxygen was being generated before it began accumulating in large amounts in the atmosphere

Lec 2 Q4: Describe the approximate timing of one max extinction, and what a possible cause of this extinction was.

Permian-Triassic Mass was one of the most severe mass extinction that happened about 252 million years ago. This extinction was caused by long term volcanic eruptions that wiped out many marine species at the time.

Lec 3 Q1: Describe why the length of the day has changed during geological time. What has happened to the length of the day in the last few years?

• The length of the day has changed because of tidal friction. The movement of the tides over the earth means water rubbing over earth, by friction, which takes energy away from earth’s orbit.

• In the last few years the length of the day have been getting shorter again meaning earth is spinning slightly faster.

Lec 3 Q2: State 6 lines of evidence for plate tectonics

• Glacial striations radiating away from Antarctica

• Fossils match across continents

• Zebra stripes on ocean floor show continental drift and sea floor spreading

• coast line of Africa + South America fit like a puzzle

• pattern of earthquakes/volcanoes -> they are everywhere around earth, uneven distribution

• Distributions of mountain ranges across earth

Lec 3 Q3: Describe how magnetic stripes on the seafloor form, and how they provide evidence for the process of sea-floor spreading.

Basalt forming at mid-ocean ridges records the direction of Earth’s magnetic field when it cools and solidifies. As Earth’s magnetic field reverses through time, newly formed crust preserves alternating band of normal and reversed polarity. The symmetrical pattern of magnetic stripes on both sides of ridges demonstrates that new sea floor is continuously created and moves outwards from the ridge axis.

Magnetic stripes on the seafloor form through a continuous process of magma eruption and magnetic recording at mid-ocean ridges

Lec 3 Q4: Give an example of a place on earth where there is a continental-continental collision zone, describe approximately what the tectonic plates are doing in this location, and the associated geological hazards/features.

The Himalayas are an example of a continental-continental collision zone. The Indian Plate is colliding with the Eurasian Plate, causing crustal shortening and uplift. This collision produces the world’s highest mountains and generates powerful earthquakes.

Himalayan Mountain Range, continental-continental tectonic plates collide, can form volcanic mountain chains, folded mountains, and deep earthquakes.

Lec 3 Q5: Describe the two main driving forces behind plate tectonics

New crust formation and heat transfer from the mantle help drive seafloor spreading at ridges. The gravitational pull of dense plates descending into subduction zones called slab pull, is a major force driving plate motion.

Lec 4 Q1: Give one example of a volcanic island made by a hotspot. Describe the approximate distribution of hotspots around the world. What features on the core-mantle boundary are thought to feed hotspots?

Hawaii is a volcanic island chain formed above a mantle hotspots. Hotspots occur on many tectonic plates throughout the world, including the pacific, Atlantic, African, and Antarctic regions. most hotspots occur away from plate boundaries and are scattered across both oceanic and continental plates.

Describe how a new ocean can form when a hotspot impinges on a continent and give one example of where this is happening at the moment on Earth.

• A mantle plume can heat and weaken continental lithosphere, producing uplift and rifiting

• continued extension pulls the continent apart until a new spreading center develops and oceanic crust forms

• the east african rift is an example of a region where this process may eventually create a new ocean basin

Write a one sentence definition of an earthquake.

And earthquake is the release of strain energy when rocks slide past each other along a fault.

Describe the different types of seismic waves, including how they travel (e.g. with a diagram showing particle motion), what order they arrive in, and which type causes the most damage.

• p waves are compressional waves that travel through solides and liquids and arrive frist because they move fastest

• s waves move particles perpendicular to the direction of travel, can only pass through solids, and arrive after p waves

• rayleigh and love waves travel along earth’s surface, arrive last, and causr the stringest shaking and most damage

Describe how we can work out where an earthquake happened using three seismometers.

the difference between p waves and s wave arrival times at a seismometer is used to determine the distance to an earthquake

a circle with that distance as tis radius is drawn around the first seismic station

the process is repeated for a second station, producing a second circle that narrows the possible locations

a third station is used so the three circles intersect at a single point, identifying the earthquake epicenter.

Lec 4 Q6: Describe the factors that control the magnitude of an earthquake. Hint: might be easiest to give the equation, and describe what term is what.

• earthquake energy release depends on the strength of the rocks invoilved in the rupture

• earthquake energy release increases as the area of the fault that slips becomes larger

• earthquakes energy release also increases with the amount of displacement, or slip, that occurs

Describe the factors that control the intensity of an earthquake in any given location.

• earthquake intensity depend on how far a locations from the earthquake source because shaking generally decreases with distance

• earthquake intensity depends on regional geology, as seismic waves travel farther through some rock types than others

• earthquake intensity depends on local ground conditions because soft sediments can amplify shaking and cause liquefaction

What type of plate boundary makes the biggest earthquakes (e.g. M9) and why can such large earthquakes occur there?

• the largest earthquakes occur at subduction-zone megathrust boundaries where one tectonic plate is forced beneath another

• megathrust faults can be hundreds of miles long, such as the Cascadia megathrust, which is about 600 miles long\

• their enormous fault area and ability to undergo large amounts of slip allow them to release huge amounts of energy during rupture

Describe 3 ways you can make a typical bay area single family home more resistant to earthquakes.

• install foundation anchors to bolt the house securely to its foundation

• install shear-transfer ties that help transfer earthquake forces through the structure

• install tension ties to improve structural continuity and reduce the chance of the house pulling apart during shaking

Describe 3 ways you can make tall skyscraper more resistant to earthquakes.

• use truss systems that strengthen the building against horizontal shear forces at its base

• install vibration-suppression systems that absorb and reduce building motion during earthquakes

• incorporate a central mass or core column, such as the shinbashira design, to dampen oscillations during strong shaking

Describe how earthquake early warning systems work – how are we able to get advanced warning? What controls how many seconds of warning we can get? Name 4 things we can do with a few seconds’ worth of warning.

Earthquake early warning systems detect the fast-moving P-waves and send alerts before the slower and more damaging waves arrive. The amount of warning depends primarily on a person's distance from the earthquake source because seismic waves require time to travel outward. A few seconds of warning can allow people to drop, cover, and hold on, stop surgeries, slow trains, and shut off gas lines.

Describe the evidence used by Andrija Mohorovičić to propose the existence of the Moho. Hint: watch the video in Lecture 6!

• Mohorovicic observed that some seismic waves arrived earlier than expected at distant stations

• he concluded that the waves were refracting through a deeper layer where seismic velocities were higher, revealing the crust-mantle boundary now called the Moho

Describe how we know that the Earth’s outer core is a liquid.

• S-waves do not travel through the outer core, indicating that it behaves as a liquid layer

• The strong refraction and shadowing of P-waves as they pass through the outer core provides additional evidence that it is liquid.

Describe why the mantle melts at mid-oceanic ridges (divergent boundaries).

• Mantle material rises toward the surface beneath mid-ocean ridges as tectonic plates move apart.

• As the mantle rises, pressure decreases while temperature remains relatively high

• This decompression causes the mantle to begin melting at depths shallower than about 75 km and produce basaltic magma.

Describe why the mantle melts at hotspots (e.g Hawaii)

• Mantle plumes bring hot mantle material upward toward Earth's surface beneath hotspots.

• The rising mantle experiences lower pressure than the surrounding mantle

• The combination of higher temperature and lower pressure produces extensive melting and magma generation.

Describe why the mantle melts at subduction zones (convergent boundaries).

• Oceanic crust altered by seawater is carried downward into the mantle at subduction zones.

• As the slab warms, hydrous minerals break down and release water into the overlying mantle.

• The added water lowers the mantle melting temperature and causes partial melting that generates magma.

Provide a one-sentence definition of viscosity, and then rank the following materials in order from lowest to highest viscosity: water, rhyolitic magma, olive oil, ketchup.

• Viscosity is the resistance of a material to flow

• From lowest to highest viscosity the order is water, olive oil, ketchup, and rhyolitic magma.

• Rhyolitic magma has the highest viscosity because its high silica content forms extensive silica chains that resist flow.

Describe two processes which can increase the SiO2 content (and thus the viscosity) of a magma.

• Fractional crystallization increases SiO₂ content by removing minerals that are relatively poor in silica from the magma.

• Crustal assimilation increases SiO₂ content when silica-rich continental crust melts and mixes with the magma.

LEC 7 Q6: Would you expect a rhyolite with 4 wt% H2O to erupt more or less explosively than a basalt with 1 wt% H2O. Explain your answer.

• A rhyolite containing 4 wt% H₂O would erupt much more explosively than a basalt containing 1 wt% H₂O.

• Its much higher silica content creates greater viscosity that traps gas bubbles, allowing pressure to build until explosive fragmentation occurs.

Describe some factors that control the explosivity of a volcanic eruption

• High concentrations of dissolved gases such as H₂O and CO₂ increase eruption explosivity by producing expanding bubbles.

• High magma viscosity caused by elevated silica content prevents gases from escaping easily and promotes explosive eruptions.

Describe what happens to magma viscosity as you undergo fractional crystallization from a basalt to a rhyolite. Hint – think about the chains.

• Fractional crystallization progressively increases the SiO₂ content of the remaining magma.

• Higher silica concentrations cause silica tetrahedra to form increasingly interconnected chains and networks within the melt.

• As these networks develop, magma viscosity increases greatly as the magma evolves from basalt to rhyolite.

How do calderas like Crater Lake, Oregon and Santorini, Greece form?

• A very large explosive eruption empties much of the magma chamber beneath the volcano.

• The overlying crust then collapses into the emptied chamber, forming a large depression called a caldera.

Your friend is very worried about an eruption at Yellowstone. What could you tell them to calm them down?

• The slides state that the probability of a Yellowstone supereruption is about 1 in 730,000, which is similar to the chance of a 1-km asteroid striking Earth

• Although its last major eruption occurred about 640,000 years ago, Yellowstone has mainly produced lava flows since then, including one around 70,000 years ago.

Describe 2 processes which can cause a volcano to erupt – i.e. go from a stable magma chamber at depth to material rising to the surface.

• Volcanic eruptions occur when pressure inside a magma chamber exceeds the strength of the rocks above it.

• Injection of new magma into a chamber increases pressure because more liquid is added to a fixed volume

• Volatile exsolution occurs when crystallization concentrates dissolved water and other gases in the remaining magma.

• As bubbles form and expand, they increase pressure in the chamber until an eruption can occur.

Describe 2 ways that pyroclastic flows can form during volcanic activity

• Pyroclastic flows can form when a lava dome collapses and sends hot fragmented rock and gas racing downslope

• Pyroclastic flows can also form when a Plinian eruption column collapses under its own weight, as occurred during the eruption of Vesuvius.

Can we stop lava flows? What approaches have been tried? What worked and what didn’t?

• Attempts to stop lava flows have included bombing lava channels, constructing barriers, and cooling lava with seawater.

• Physical diversion and cooling methods have had some success, whereas bombing lava flows has generally been ineffective.

Describe what happens to emitted SO2 gas after it is released into the atmosphere and why SO2 emission present a health issue to humans. Name 4 other gases released from volcanoes. Which ones impact human health?

• Sulfur dioxide released by volcanoes reacts in the atmosphere to form sulfuric acid and sulfate aerosols.

• These fine particles are hazardous because they degrade air quality and can cause respiratory health problems.

• Volcanoes release H₂O, CO₂, chlorine-bearing gases, and fluorine-bearing gases in addition to SO₂

• CO₂, chlorine gases, and fluorine gases can negatively affect human health, while high concentrations of CO₂ can even cause asphyxiation.

Describe what a lahar is and how it forms. Name one volcano and/or area that has been affected by a lahar disaster.

• A lahar is a fast-moving mixture of water and volcanic rock fragments that flows down the slopes of a volcano through valleys and stream channels.

• Lahars can form when volcanic activity melts snow and ice, when heavy rain mobilizes fresh ash deposits, or when rainfall remobilizes older volcanic deposits.

• The 1985 eruption of Nevado del Ruiz in Colombia produced lahars that destroyed the town of Armero and killed more than 23,000 people.

What is a volcanic hazard map? How could a city resident use a volcanic hazard map? A government official?

• A volcanic hazard map identifies areas at risk from hazards such as lahars, lava flows, ashfall, and pyroclastic flows using information from past eruptions and topography.

• A city resident can use a hazard map to determine whether their home is in a dangerous area and identify evacuation routes before an eruption.

• A government official can use hazard maps to guide land-use planning, emergency response plans, and infrastructure development in volcanic regions.

Describe 3 methods that can be used to monitor active volcanoes.

Describe 2 ways in which tsunamis differ from normal ocean waves.

Describe 3 processes that can cause tsunamis and give a historical example of a tsunami caused by each process.

State 3 warning signs that could alert you to get to high ground because a tsunami is on its way.

What is the purpose of vertical evacuation towers? Which coastal communities benefit most from them? Hint: think about topography!

Why did the Indonesian tsunami in 2004 kill so many people?

(from the reading) Describe some of the lines of evidence pointing to a large Cascadia Tsunami and earthquake in 1700 AD.