The Movers and Shakers

Review: The Movers and Shakers

Key Terms

  • abyssal plains: Flat areas on the ocean floor, typically deep under water.
  • accretionary wedge: A mass of sediment that builds up at a subduction zone, incorporating sediments from the ocean floor.
  • active margin: A continental margin that is characterized by tectonic activity, often featuring deep ocean trenches due to subduction.
  • Aleutian-type mountains: Formed from the collision of two oceanic plates.
  • Andean-type mountains: Created when an ocean plate collides with a continental plate at an active margin.
  • arc-continent mountains: Mountains formed by the collision of an oceanic arc with a continental landmass, often through a process known as terrane accretion.
  • atolls: Ring-shaped coral reefs that form around sinking islands.
  • buoyancy: The ability of an object to float in a fluid, which affects how mountains 'float' on the Earth’s tectonic plates.
  • chemoautotroph: Organisms that produce energy by oxidizing inorganic substances, commonly found near hydrothermal vents.
  • continental margin: The zone between the continental crust and the oceanic crust, consisting of the continental shelf, slope, and rise.
  • continental rise: The gently sloping area at the base of a continental slope.
  • continental shelf: The submerged extension of the continent, featuring shallow waters.
  • continental slope: The steep descent between the continental shelf and the ocean floor.
  • coral reefs: Underwater structures formed from the calcium carbonate skeletons of coral polyps.
  • deform fault-block mountains: Mountains formed from faults that cause blocks of crust to be lifted or dropped.
  • faulting: The fracturing of the Earth's crust that leads to the displacement of rock formations.
  • folding: The bending of rock layers due to tectonic forces.
  • guyots: Submerged, flat-topped mountains or volcanoes.
  • isostasy: The equilibrium between the Earth's crust and the mantle beneath it, affecting land elevation.
  • isostatic adjustment: The process by which the Earth's crust rises or sinks in response to changes in surface load.
  • mountain: A large landform that rises prominently above its surroundings.
  • mountain belt: A series of connected mountain ranges.
  • mountain range: A series of peaks connected by high ground.
  • orogenesis: The process of mountain formation, particularly through tectonic plate interactions.
  • passive margin: A continental margin that does not have tectonic activity, often featuring wider continental shelf areas.
  • rift zones: Areas where the Earth's crust is stretching and thinning.
  • seamounts: Underwater mountains formed by volcanic activity.
  • shelf break: The transition between the continental shelf and the continental slope.
  • sonar: A technology used to map ocean floors and identify underwater features.
  • submarine canyon: Deep, steep-sided valleys cut into the seabed of the continental slope.
  • terrane: A fragment of the Earth’s crust with a distinct geological history.
  • terrane accretion: The process of landmasses being added to continental regions through plate tectonics.
  • topography: The arrangement of the natural and artificial physical features of an area.

Objectives

Earth Science 4.4.1
  • Understand the features of the ocean floor and their formation.
  • Analyze the role of ocean ridges in plate tectonics interpretation.
  • Explain how life exists near hydrothermal jets.
  • Describe the basic physical and chemical composition of the ocean floor.

Ocean Commotion

Ocean Features Classification and Formation

  • The ocean floor features resemble continent features, including the continental margin which consists of:
    1. Continental shelf: Shallow area adjacent to coast.
    2. Continental slope: Steep drop-off.
    3. Continental rise: Gentle incline that leads to the sea floor.
Active vs. Passive Margins
  • An active margin occurs where tectonic plates collide, often leading to the formation of deep ocean trenches from subduction.
  • A passive margin is characterized by a gentle slope that leads to a continental rise without tectonic activity.

Submerged Features

  • Guyots and seamounts refer to submerged mountains.
  • Abyssal plains are expansive flat areas found at the sea floor.
  • Coral reefs support marine life and can form into atolls around sinking mountains.

Hydrothermal Vents

  • Chemoautotrophs are crucial as they thrive near hydrothermal vents, allowing other organisms to exist in this ecosystem.
  • Hydrothermal vents release warm, sulfur-rich water, influencing local marine biology.
  • The ocean crust primarily consists of basalt, with a sediment layer of approximately 1 km thick.

Seafloor Spreading and Plate Tectonics

  • Seafloor spreading occurs at the rift zones of ocean ridges, providing evidence for plate tectonics.
  • Ocean crust age is approximately 200 million years at most, highlighting the dynamic nature of oceanic environments.

Ain't No Mountain High Enough

Understanding Mountains

  • Earth is categorized as a dynamic planet where tectonic plate movements reshape the surface continually.
  • Orogenesis or mountain formation occurs through rock faulting and folding combined with tectonic activity.
Types of Mountain Formation
  • Andean-type mountains result from the collision between an oceanic and a continental plate.
  • Arc-continent mountains form through terrane accretion, such as those in the North American Cordillera.
  • Aleutian-type mountains arise from two colliding oceanic plates, with the Aleutian Islands serving as a prominent example.
  • Fault-block mountains, like the Grand Tetons, are unique as they form from plate spreading.

Forces Supporting Mountains

  • Mountains remain buoyant due to the balance between their buoyancy properties and the pull of gravity, known as isostasy.

Creaks and Hazards

Key Terms

  • active volcano: A volcano that has erupted recently and may erupt again.
  • aftershocks: Smaller earthquakes following the main quake.
  • caldera: A large crater formed by a volcanic eruption.
  • central vent: The main opening in a volcano where magma is expelled.
  • cinder cone volcanoes: Small, steep-sided volcanoes formed from tephra.
  • composite cone volcanoes: Volcanoes formed from alternating layers of lava and tephra, known for their explosive eruptions.
  • dormant volcano: A volcano that has not erupted in a long time but could potentially erupt.
  • epicenter: The point on the earth's surface directly above the earthquake's origin.
  • explosive eruption: Eruptions that involve significant explosive discharge of magma.
  • extinct volcano: A volcano that is unlikely to erupt again.
  • foreshocks: Smaller quakes that precede a larger earthquake.
  • intensity: Measure of the effects of an earthquake at different locations.
  • magma: Molten rock beneath the earth's surface.
  • magnitude: Magnitude of an earthquake is a measure of energy released.
  • P waves: Primary waves that compress and expand the ground.
  • S waves: Secondary waves that move in a shear motion.
  • tsunami: A large ocean wave typically caused by an underwater earthquake.

Volcanic Activity

  • Volcanoes eject materials when magma pressure builds enough to erupt. The type and violence of eruption hinge on the viscosity of the magma.
  • Higher magma viscosity correlates with greater eruption pressure and explosive potential.
  • Magma viscosity relates to silica content – the more silica, the higher the viscosity and eruption pressure.
Volcano Classification
  • Subduction zone volcanoes typically produce explosive eruptions and are commonly found along the Pacific Ring of Fire.
  • Shield volcanoes, like those in Hawaii, have low viscosity magma, leading to gentle and frequent eruptions.
  • Composite cone volcanoes (such as Mount St. Helens) have highly explosive eruptions characterized by pyroclastic flows.
Caldera Formation
  • A caldera forms when the roof of a volcano collapses due to magma evacuation, creating a large crater, like that found in Yellowstone National Park.
  • Lava domes are formed by the slow extrusion of viscous lava in the craters of larger volcanoes.

Brake for Quakes

Earthquake Dynamics

  • Earthquakes occur when tectonic plates shift along faults. The point of failure underground is termed the focus, while the point directly above it on the surface is the epicenter.
Understanding Seismic Waves
  • Seismic waves include:
    • P waves (Primary waves): Fastest waves that travel through the earth material.
    • S waves (Secondary waves): Travel slower, can only move through solids.
    • L waves (Surface waves): Slowest, travel along the Earth’s surface.
  • The intensity of an earthquake's effects diminishes with distance from the focus.
Measuring Earthquakes
  • Magnitude indicates the strength of an earthquake, typically assessed using the Richter scale which is logarithmic. Each whole number increase represents a tenfold increase in measured amplitude and approximately 32 times more energy release.
Tsunami Mechanics
  • Tsunamis are often initiated by underwater earthquakes, presenting great danger when reaching shore. As they approach land, they tend to slow down, becoming taller and more closely spaced.
Earthquake Prediction
  • Currently, short-term earthquake prediction is unfeasible, although long-term assessments provide some predictive capabilities on possible earthquake occurrences.

Sculpting Earth

Weathering and Erosion

Key Terms
  • abrasion: The wearing away of rock surfaces due to mechanical action.
  • chemical weathering: Changes in rock composition due to chemical reactions, including oxidation and carbonation.
  • glacial drift: Rock debris transported and deposited by glaciers.
  • mass wasting: Movement of soil or rock due to gravity.
  • physical weathering: Breakdown of rocks without chemical change, usually through factors like freeze-thaw cycles.
  • U-shaped valleys: Valleys shaped by glacial erosion.

Weathering Processes

  • Weathering can be categorized into:
    • Physical Weathering: Breakage into smaller pieces through processes like frost wedging, biological activity, or thermal expansion.
    • Chemical Weathering: Alteration of rock composition via reactions, leading to soil formation crucial for various ecosystems.
Erosion Mechanisms
  • Erosion is the transport of materials through agents like wind and water. Bare land is prone to severe erosion, illustrated historically by the Dust Bowl.
  • Mass wasting involves the gravitational movement of earth materials, categorized into types including:
    • Soil creep: Slow, gradual movement of soil.
    • Mudflow: Rapid flow of water-saturated materials.
    • Rockslide: Quick tumble of rock debris.
    • Avalanche: Fast flow of material, typically snow or ice.

Karst Topography

Formation Process
  • Karst topography arises from the chemical weathering of limestone when dissolved by carbonic acid from rainfall mixed with CO2 from soil.
  • This process creates various formations such as caves, sinkholes, and limestone pavements.
Cave Features
  • Caves develop over millions of years and produce speleothems, including:
    • Stalactites: Hang from ceilings of caves, formed from mineral deposits.
    • Stalagmites: Build from the ground up as minerals accumulate from dripping water.
Sinkhole Dynamics
  • Sinkholes can form either gradually (gentle slopes) or suddenly (steep slopes), resulting in circular depressions in the ground.

At a Glacial Pace

Glacier Types and Dynamics

  • Two main types of glaciers: Alpine glaciers and ice sheets.
  • Alpine glaciers are found in mountainous regions, while ice sheets cover large parts of Greenland and Antarctica, acting as polar ice caps.
  • Glaciers form when snow compacts due to its weight, transitioning to ice, allowing for movement through basal slip and internal plastic flow.
Glacial Erosion and Features
  • Glaciers carve landscapes, leading to:
    • U-shaped valleys: Indicating past glacial movement.
    • Cirques, horn peaks, and fjords: Erosional features formed by glaciers.
Retreat and Depositional Features
  • As glaciers retreat, they deposit various features:
    • Glacial erratics: Large boulders moved by glacial activity.
    • Moraines: Accumulations of debris along the sides or at the ends of glaciers.
    • Kettles: Depressions formed from melting ice blocks.
    • Drumlins: Egg-shaped hills formed beneath moving glaciers.
    • Eskers: Long, winding ridges formed from sediment left by meltwater.

Ice Age Evidence

  • The last Ice Age peaked approximately 20,000 years ago, impacting sea levels and allowing land bridges (e.g., between Russia and Alaska) due to lower ocean levels.
  • Ice ages are theorized to result from continental positions influenced by plate movements, with orbital variations also playing a role.
  • Melting ice sheets would drastically raise ocean levels, impacting coastal habitation globally.