ERTH STUDY GUIDE

These flashcards encompass key terms and definitions related to plate tectonics, volcanism, earthquakes, and climatic phenomena, aiding in exam preparation.

Divergent Boundaries

These are areas where two tectonic plates move away from each other. As the plates pull apart, magma from the Earth's mantle rises to the surface, creating new crustal material. This process is known as seafloor spreading. Common landforms associated with divergent boundaries include:

• Mid-ocean ridges: Underwater mountain ranges like the Mid-Atlantic Ridge, where new oceanic crust is continuously formed.

• Rift valleys: Elongated depressions that form on continents as landmasses begin to split apart, such as the East African Rift Valley.

Convergent Boundaries

These are boundaries where two tectonic plates collide or move towards each other, resulting in the destruction of old crust or the formation of mountains. The outcomes depend on the type of crust involved:

• Oceanic-Continental Convergence: The denser oceanic plate subducts beneath the less dense continental plate. This creates a deep oceanic trench on the ocean side and a volcanic mountain range on the continent, like the Andes Mountains in South America, formed by the subduction of the Nazca Plate beneath the South American Plate.

• Oceanic-Oceanic Convergence: One oceanic plate subducts beneath another, forming a deep oceanic trench and an island arc (a chain of volcanic islands) parallel to the trench. Examples include the Mariana Trench and the Mariana Islands in the western Pacific.

• Continental-Continental Convergence: When two continental plates collide, neither plate subducts significantly due to their similar densities. Instead, the crust crumples, thickens, and is uplifted to form vast mountain ranges, such as the Himalayas, where the Indian Plate is colliding with the Eurasian Plate.

Transform Boundaries

At transform boundaries, two tectonic plates slide horizontally past each other. This movement does not create or destroy crust but instead results in significant shear stress. The primary feature associated with these boundaries is a transform fault, which is a fracture in the Earth's crust along which the two sides move past each other. This movement often causes frequent but shallow earthquakes. A prominent example is the San Andreas Fault in California, where the Pacific Plate slides past the North American Plate.

Subduction Zone

A subduction zone is a geological area where one tectonic plate descends beneath another into the Earth's mantle. This process occurs typically at convergent boundaries where one plate (usually denser oceanic crust) is forced underneath a less dense plate. Key features and processes associated with subduction zones include:

• Deep Oceanic Trenches: Formed at the point where the subducting plate bends downwards, these are the deepest parts of the ocean floor, such as the Mariana Trench.
• Volcanic Arcs: As the subducting plate descends, it heats up and releases water, which lowers the melting point of the surrounding mantle rock. This generates magma that rises to form a chain of volcanoes on the overriding plate (either a continental volcanic arc or an island arc).
• Earthquakes: Powerful earthquakes, including megathrust earthquakes, often occur along the interface of the two plates as they grind against each other.
• Recycling of Crust: Subduction zones are crucial for the recycling of oceanic crust back into the mantle.

Oceanic Crust

Oceanic crust is the Earth's outer layer found beneath the oceans. It is relatively thin, typically ranging from 5 to 10 km in thickness, and is composed primarily of mafic rocks like basalt and gabbro, making it denser than continental crust. Oceanic crust is continuously formed at mid-ocean ridges through volcanism and seafloor spreading, and it is subsequently recycled back into the mantle at subduction zones. Consequently, it is generally much younger than continental crust, with the oldest oceanic crust being around 200 million years old.

Continental Crust

Continental crust is the Earth's outer layer that forms the continents and continental shelves. It is significantly thicker than oceanic crust, ranging from 30 to 70 km, and is composed of a more varied range of felsic to intermediate rocks, such as granite and andesite, making it less dense than oceanic crust. Due to its lower density, continental crust is buoyant and resists subduction, which is why it is generally much older and more geologically complex than oceanic crust. The oldest continental crustal rocks are billions of years old.

Fault

A fault is a fracture or a zone of fractures in the Earth's crust where there has been observable displacement or sliding of the rock blocks on either side. Faults are formed in response to tectonic stresses (tension, compression, shear) acting on the crust and are often the sites of earthquakes. The main types of faults include:

• Normal Faults: Result from tensional forces where the hanging wall moves down relative to the footwall (e.g., in rift valleys).
• Reverse Faults (or Thrust Faults): Result from compressional forces where the hanging wall moves up relative to the footwall (e.g., in mountain building areas at convergent boundaries).
• Strike-Slip Faults: Result from shear forces where blocks of rock slide horizontally past each other, parallel to the fault line (e.g., at transform boundaries like the San Andreas Fault).

Volcanic Arc

A volcanic arc is a chain of volcanoes that forms on the overriding tectonic plate above a subducting oceanic plate. The process begins as the subducting plate descends into the mantle, releasing water and other volatile compounds that lower the melting point of the overlying mantle wedge. This generates magma, which then rises to the surface to form volcanoes. Volcanic arcs can be:

• Continental Volcanic Arcs: Form on continental crust, such as the Cascade Range in the Pacific Northwest of North America, where the Juan de Fuca Plate subducts beneath the North American Plate.
• Island Arcs: Form on oceanic crust, appearing as a curved chain of volcanic islands, like the Japanese archipelago or the Aleutian Islands.

Volcanism

Volcanism refers to the process by which molten rock (magma), volcanic ash, and gases are erupted from the Earth's interior onto its surface or into the atmosphere. This activity is primarily driven by internal heat and is heavily influenced by magma composition, the amount of dissolved gases, and the tectonic setting. Volcanism occurs in several key tectonic environments:

• Divergent Boundaries: Magma rises to fill the gap as plates separate, forming new oceanic crust at mid-ocean ridges (e.g., Iceland).
• Convergent Boundaries: Subduction zones generate magma that forms volcanic arcs (e.g., Mount St. Helens, Mount Fuji).
• Hotspots: Isolated plumes of magma rising from the mantle can create volcanoes far from plate boundaries (e.g., the Hawaiian Islands).

Difference between tsunami on open ocean vs near shore

A tsunami is a series of extraordinarily long ocean waves generated by large-scale disturbances that displace a massive volume of water, such as powerful underwater earthquakes (especially megathrust events), volcanic eruptions, landslides, or meteor impacts.

• In the Open Ocean: When traveling across the deep open ocean, tsunami waves possess very long wavelengths (often hundreds of kilometers) and travel at extremely high speeds (several hundred kilometers per hour), comparable to a jet plane. However, their amplitude (wave height) is very small, often just a few tens of centimeters to a meter, making them largely undetectable by ships.
• Close to Shore (Shoaling Effect): As a tsunami approaches the coastline and enters shallower water (a process called shoaling), the interaction with the seafloor dramatically changes its characteristics. The wave's speed significantly decreases, but its energy is conserved and compressed into a smaller volume. This causes the wave height (amplitude) to increase dramatically, sometimes reaching tens of meters. The wavelength shortens, and the wave steepens, transforming into a towering, destructive wall of water or a rapidly rising tide that can inundate coastal areas with immense force.

Coriolis Force

The Coriolis force is an apparent force that deflects moving objects (like air masses, ocean currents, and projectiles) from a straight path due to the Earth's rotation. This effect is a consequence of inertia and the observer's rotating frame of reference on Earth.

• Deflection: It causes moving objects to deflect to the right of their initial direction in the Northern Hemisphere and to the left in the Southern Hemisphere.
• Magnitude: The strength of the Coriolis force increases with the velocity of the moving object and with latitude, being zero at the equator and maximum at the poles.
• Impacts: This force is fundamental in shaping global weather patterns by influencing:
  • Wind patterns: It causes winds to blow around high and low-pressure systems (e.g., clockwise around highs in NH).
  • Ocean currents: It helps drive large-scale ocean gyres.
  • Storm rotation: It is responsible for the characteristic cyclonic (counter-clockwise in NH) and anticyclonic (clockwise in NH) rotation of storms like hurricanes and tornadoes.

Greenhouse Effect

The Greenhouse Effect is a natural process where certain gases in Earth's atmosphere trap heat, warming the planet's surface to a temperature suitable for life. It works as follows:

• Solar Radiation: Short-wavelength (visible light and ultraviolet) radiation from the Sun easily penetrates the atmosphere and is largely absorbed by Earth's surface, causing it to warm up.
• Infrared Emission: The warmed Earth's surface then emits longer-wavelength (infrared) radiation back towards space.
• Gas Absorption and Re-emission: Specific atmospheric gases, known as greenhouse gases (e.g., carbon dioxide (CO2), methane (CH4), water vapor (H2O), nitrous oxide (N2O)), are transparent to incoming shortwave radiation but absorb and re-emit much of the outgoing longwave infrared radiation. A portion of this re-emitted infrared radiation is directed back towards the Earth's surface, effectively trapping heat and preventing it from escaping into space.
• Enhanced Greenhouse Effect: Human activities, primarily the burning of fossil fuels and deforestation, have significantly increased the concentrations of greenhouse gases in the atmosphere, leading to an 'enhanced' greenhouse effect and contributing to global warming.

Positive Feedback Loop

A positive feedback loop is a process within a system that amplifies or accelerates its initial effect, leading to an increase in the magnitude of the change. It drives the system further in the same direction.

• Example (Ice-Albedo Feedback): As global temperatures rise, ice and snow (which are highly reflective, having a high albedo) melt. This exposes darker land or ocean surfaces beneath, which absorb more solar radiation. This increased absorption causes further warming, leading to more melting, thus amplifying the initial warming trend.

Negative Feedback Loop

A negative feedback loop is a process within a system that counteracts or reduces the initial change, thereby stabilizing the system and helping it return to equilibrium. It works to diminish the output of a system.

• Example (Cloud Formation): If Earth's temperature increases, more water evaporates, potentially leading to increased cloud formation. Low clouds, being highly reflective, can then reflect more incoming solar radiation back to space, which would lead to a cooling effect, counteracting the initial warming. (Note: The role of high clouds is more complex, as they can trap heat).

Tornado

A tornado is a rapidly rotating, intensely violent column of air that extends from the base of a cumulonimbus cloud (a severe thunderstorm) to the ground. These relatively small-scale, short-lived, yet extremely destructive weather phenomena are characterized by:

• Formation: They typically form in association with supercell thunderstorms, which have a rotating updraft (mesocyclone) caused by strong wind shear.
• Appearance: Often visible as a funnel-shaped cloud, sometimes obscured by rain or debris.
• Wind Speeds: Capable of producing the most violent winds on Earth, exceeding 300 mph (480 km/h), resulting in highly localized and extreme pressure drops.
• Path and Duration: Usually have very erratic and narrow paths (often less than 1 km wide) and short lifespans (minutes to tens of minutes), though some can persist for over an hour. They are a product of atmospheric instability and powerful convection.

Hurricane

A hurricane (also known as a typhoon in the Pacific or a tropical cyclone in the Indian Ocean) is a large, rotating, organized storm system that forms over warm tropical or subtropical ocean waters and can persist for days to weeks. Key characteristics include:

• Formation Conditions: Requires warm ocean waters (>26.5°C or 80°F) to a significant depth, high humidity, low vertical wind shear, and pre-existing atmospheric disturbances.
• Energy Source: Draws energy through the evaporation of warm ocean water and the release of latent heat during condensation in rising air.
• Structure: Features a distinct low-pressure center called the 'eye' (a calm, clear area), surrounded by the 'eyewall' (the most intense part of the storm with the strongest winds and heaviest rainfall), and spiral 'rainbands' extending outward.
• Size and Duration: Much larger than tornadoes (hundreds of kilometers in diameter) and can last for extended periods, traveling significant distances. Their paths are generally more predictable, guided by large-scale atmospheric patterns. While central pressure is very low, it's spread over a broader area compared to a tornado.

High-Pressure System

A high-pressure system, also known as an anticyclone, is an atmospheric system characterized by a mass of descending (sinking) air. As air sinks, it warms adiabatically and its relative humidity decreases, suppressing cloud formation. This typically leads to:

• Clear Skies: Often brings calm, clear, and dry weather conditions.
• Wind Direction: In the Northern Hemisphere, winds diverge outward and flow clockwise around the center of a high-pressure system. In the Southern Hemisphere, winds diverge outward and flow counter-clockwise.
• Stability: High-pressure systems are generally associated with atmospheric stability and fair weather.

Low-Pressure System

A low-pressure system, also known as a cyclone, is an atmospheric system characterized by a mass of ascending (rising) air. As air rises, it cools adiabatically, leading to condensation, cloud formation, and often precipitation. This typically results in:

• Cloudy/Stormy Skies: Often associated with unsettled, cloudy, and wet weather conditions, including rain, snow, or storms.
• Wind Direction: In the Northern Hemisphere, winds converge inward and flow counter-clockwise around the center of a low-pressure system. In the Southern Hemisphere, winds converge inward and flow clockwise.
• Instability: Low-pressure systems are generally associated with atmospheric instability and adverse weather.

How gases in the atmosphere interact with long and short wavelength radiation

The interaction of atmospheric gases with different wavelengths of radiation is fundamental to Earth's energy balance and the greenhouse effect:

• Short-wavelength (solar) radiation: This radiation, primarily visible light and ultraviolet light from the Sun, passes relatively unimpeded through most atmospheric gases. It is absorbed by the Earth’s surface, warming it up.
• Long-wavelength (infrared) radiation: The warmed Earth's surface then re-emits this energy as long-wavelength infrared radiation. Certain atmospheric gases, known as greenhouse gases (e.g., carbon dioxide, water vapor, methane), are highly effective at absorbing this outgoing infrared radiation. These gases then re-radiate the absorbed energy in all directions, including back towards Earth’s surface.
• Energy Balance and Temperature: This absorption and re-emission process by greenhouse gases traps heat within the Earth's lower atmosphere, leading to the overall warming of the planet (the greenhouse effect). The selective transparency of the atmosphere to shortwave radiation and its opacity to longwave radiation is crucial for maintaining Earth's habitable temperatures.

Differences between tornadoes and hurricanes

While both tornadoes and hurricanes are rotating storm systems, they differ significantly in their scale, formation, intensity, duration, and structure:

• Scale:
  • Tornadoes: Smallest scale, typically a few tens of meters to a few kilometers wide.
  • Hurricanes: Largest scale, typically hundreds of kilometers (diameter) in width.
• Formation Environment:
  • Tornadoes: Form over land, within severe thunderstorms (supercells) due to atmospheric instability and strong wind shear.
  • Hurricanes: Form over warm tropical/subtropical ocean waters, requiring specific oceanic and atmospheric conditions.
• Duration:
  • Tornadoes: Short-lived, typically lasting minutes to tens of minutes.
  • Hurricanes: Long-lived, often lasting days to weeks.
• Energy Source:
  • Tornadoes: Draw energy from the powerful updrafts and rotational energy (wind shear) within a severe thunderstorm.
  • Hurricanes: Draw energy from the latent heat released as vast amounts of water vapor evaporate from warm ocean surfaces and then condense in the storm's core.
• Wind Intensity / Pressure Drop:
  • Tornadoes: Possess the most intense winds on Earth (up to 300+ mph) within a very small area, leading to an extremely steep and localized pressure drop.
  • Hurricanes: While powerful (winds 74+ mph), their wind speeds are generally lower than the most extreme tornadoes, and their central pressure drop is lower but extends over a much broader region.
• Structure:
  • Tornadoes: A narrow, violent vortex, often funnel-shaped, extending from cloud to ground.
  • Hurricanes: A highly organized system with a distinct eye, eyewall, and spiral rainbands.
• Path:
  • Tornadoes: Highly erratic and unpredictable, with narrow, localized paths.
  • Hurricanes: More steady and predictable tracks, guided by larger-scale atmospheric steering currents.