Intro to Earth Science Midterm (GEOG 1120-001)

Mantle

Earth's thick middle layer beneath the crust, made mostly of hot, solid rock rich in magnesium and iron

Asthenosphere

The hot, plastic layer beneath the lithosphere; its movement helps drive plate motion, and unusually high activity can bring magma up to form volcanoes and islands

Crust

The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements

Oceanic Crust

Thin, dense crust that forms the ocean floor; it is mostly basaltic (around ~35 km thick)

Continental Crust

Thicker, less-dense crust that forms the continents (around ~7 km thick)

Felsic

Refers to light coloured, igneous rocks with higher silica composition, or the minerals that make up those rocks, including quartz, feldspar, and muscovite mica

Mafic

Refers to darker, igneous rocks with lower-silica composition, or the minerals that make up those rocks, including olivine, pyroxene, amphibole, and biotite mica

Lithosphere

Earth's rigid, brittle outer layer, made of the crust and uppermost mantle that is broken into tectonic plates

Tectonic Plates

Large pieces of the lithosphere that move relative to one another

Plate Tectonics

The theory that explains how tectonic plates move, and how they form features such as mountains and contributes to earthquakes and volcanoes

Plate Boundaries

Places where tectonic plates meet and move relative to one another, including, divergent, convergent, and transform boundaries

Divergent Boundaries

Places where plates pull apart, creating rift valleys on continents and spreading plates to allow lava to rise and create new rock beneath the ocean

Mid Oceanic Ridges (a.k.a. Spreading Center)

Long underwater features formed at oceanic divergent boundaries, where plates spread apart and rising lava cools to form new oceanic crust

Fault Block Mountains

Formed when the crust is pulled apart and faults leave some blocks of rock higher than the surrounding land

Rift Valleys

A long, low valley formed when the crust pulls apart and a block of land drops down between faults

Convergent Boundaries

Place where two plates come together, casing subduction or collision

Subduction Zones

An area where an oceanic plate sinks beneath another plate. The plate can lock as it descends, allowing stress to build and potentially release as large earthquakes. Moisture from the oceanic plate can help the rock melt, producing magma that can rise and form volcanoes

Benioff Zone

The area where earthquakes occur as one plate subducts beneath another (commonly used evidence for plate tectonics)

Earthquakes

Shaking caused when built-up stress is released as rocks suddenly move along a fault

Volcanoes

Place where lava erupted at the surface

Fold Mountains

Mountains formed when rock layers are compressed and folded as plates push together

Terranes

Pieces of Earth's crust with similar rock types attached to a continent as plates move

Juan De Fuca Plate

An oceanic plate that is sliding beneath the North American Plate, helping form mountains and volcanoes along the coast

North American Plate

The continental plate beneath much of North America; along the coast, the Juan de Fuca Plate pushes beneath it

Continental-to-Continental Boundary

A convergent boundary where two thick continental plates collide, crumpling and uplifting the crust to form fold mountains

Oceanic-to-Oceanic Boundary

Where a dense oceanic plate subducts beneath a less dense oceanic plate, causing an island arc to form on the overriding plate

Island Arcs

Place where oceanic-oceanic subduction causes volcanoes to form on an overriding oceanic plate, making a chain of active volcanoes

Transform Boundaries

Place where two plates slide past each other, creating strike slip faults

Dome Mountains

Mountains formed when magma pushes the crust upward; some form when intrusive igneous rock is later exposed by erosion

Composite Volcanoes (a.k.a. Stratovolcano)

Intermediate volcanoes made of layers of lava flows, pyroclastic material, and other deposits, and can have both flowing and explosive eruptions

Shield Volcanoes

Broad, gently sloping volcanoes formed by hot, runny mafic (basaltic) lava that lets gas escape easily, making eruptions less explosive than felsic eruptions

Plug Dome (a.k.a. Lava Dome)

Very steep sided volcanic feature formed by higher viscosity, higher-silica lava

Lava

Liquid rock on the Earth's surface

Magma

Liquid rock beneath the Earth's surface

Ring of Fire

A belt of volcanoes around the Pacific Ocean, mostly associated with subduction zones

Hot Spots

Areas of unusually high activity where magma rises to form volcanoes, sometimes creating chains of islands as a plate moves over them

Geologic Principles

The rules in which internal Earth forces and rock resistance interacting over time to shape the physical landscape (original horizontality, superposition, and cross cutting relationships)

Original Horizontality

Layered sediments are generally laid down flat at their formation, turning into rock over time

Superposition

In unaltered landforms, the rocks on the bottom are older than the rocks on the top

Cross Cutting Relationships

Any feature that cuts across or disrupts a rock body or landform must be younger than the rocks or structures it interrupts

Stress

Force applied to an object, typically dealing with forces within the Earth

Tension

Stresses that pull objects apart into a larger surface area or volume (stretching forces)

Compression

Stresses that push objects together into a smaller surface area or volume (contracting forces)

Shear Stress

Stresses that slide objects against each other in a horizontal motion

Dip and Strike

A strike is a horizontal line on a dip, telling geologists which way the rock layer is traveling across the country

Dip Slope

The slope parallel to the dip

Scarp Slope

The slope with the "edges" of rock layers (opposite to the dip slope)

Cuesta

An asymmetrical mountain or ridge caused by uplifting of rock due to compression (located between a dip slope and a scarp slope)

Anticline

An arch-shaped curve of rock layers made by compressive stress

Syncline

A downward-curving of rock layers made by compressive stress

Joint

A natural crack or fracture in a rock where the rock has not slid or moved apart

Fault

A feature where two blocks of bedrock move past each other during earthquakes

Normal Fault

The result of tension, pulling the land apart and causing the land's surface to lengthen with vertical displacement

Reverse Fault

The result of compression, pushing the land together and shortening the land's surface with vertical displacement

Thrust Fault

A type of reverse fault that has a low dip angle, generally less than 45^o

Strike-Slip Fault

The result of shear force, sliding each block of rock in opposite directions horizontally

Transform Fault

A specific type of strike-slip fault that forms an active boundary connecting 2 tectonic plates

Horst

The raised block of land between faults in a rift valley

Graben

The block of land that has dropped down between faults

Chemical Weathering

Breaking down of mineral material via chemical methods, like dissolution and oxidation

Decomposition

The biological and chemical process by which dead organic substances are broken down into simpler organic or inorganic matter and put back into the Earth

Carbonation

A natural process where CO² combines with water to make a weak acid, carbonic acid, which dissolves the calcium carbonate in limestone, resulting in features such as karst topography, caves, sink holes, dolines, stalactites, and stalagmites

Karst Topography

Carbonate rocks which dissolve, leaving behind holes which affect the landscape

Caves

Underground channels formed as water dissolves limestone

Sinkholes

An underground cave or tunnel gets larger and the surface above collapses into it

Dolines

A closed, drainless depression or hollow in karst topography

Stalactites

The calcite that grows from the ceiling of a cave downwards, creating a rock formation

Stalagmites

The calcite that builds up on the floor of a cave, creating a rock formation

Oxidation

Certain metallic elements (like iron) take in oxygen, causing reactions like rust

Hydrolysis

Water breaking into ions and replacing ions in minerals; a major type of chemical weathering in silicates

Hydration

The addition of water to the crystal structure of certain minerals creating a new mineral

Physical (a.k.a. Mechanical) Weathering

The physical breakdown (weathering) of bedrock by processes such as pressure, ice expansion, etc.

Disintegration

The result of physical weathering

Frost Shattering (a.k.a. Freeze Thaw Weathering)

Water repeatedly freezes inside the cracks in rocks, which forces the rock to further separate, resulting talus slopes (a.k.a. screes)

Talus (a.k.a. Scree)

Loose blocks of rock that fall down from steep surfaces and cover slopes

Salt Weathering (a.k.a. Haloclasty)

Salt crystals grow inside rock pores as water gets into the rocks' cracks, cools and evaporates the water's salt, to finally precipitate, producing crystals. This cycle repeats many times

Crystallization

The process of liquid rock solidifying into solid rock. Because liquid rock is made of many components, the process is complex as different components solidify at different temperatures

Differential Thermal Expansion

Different rocks take longer to heat up than others

Granular Disintegration

The physical state of the rock crumbling apart into tiny, individual sand-sized grains or crystals over time

Spalling

Similar to sheeting, although the outer layer of rocks is peeling into thin flakes

Pressure Release Jointing

Cracks that form in rocks as heavy overlying materials erode, allowing the rock underneath to expand upward and fracture

Exfoliation (a.k.a. Sheeting)

A type of mechanical weathering in which outer layers of rock peel off, parallel to the surface, and fracture off

Biological Weathering

A result of biological action can be both physical and chemical

Erosion

The transport and movement of weathered sediments

Differential Weathering

Different rocks weathering at different rates under the same condition

Hoodoo

A more resistant cap rock protects the weaker underlying rock from weathering

Mesa

A much larger version of a butte (the result of resistant rock layers protecting the underlying softer layers from erosion)

Butte

The result of resistant rock layers protecting the underlying softer layers from erosion

Step Topography

A stair-step landscape formed as harder rock resists weathering more than softer rock

Explain how tectonic plates move, and the evidence for plate tectonics

Tectonic plates move because they float on the asthenosphere, driven by internal heat and gravity. Evidence includes:

• Measuring Stations → Measurements indicate Vancouver Island and the Okanagan are getting closer as the plates slowly push together

• Offset Land Features → The San Andreas Fault show that the road and stream have visibly shifted

• Volcanic Island Chain → The Hawaiian Islands and seamounts form a chain of volcanoes as the Pacific Plate is moving over a stationary hotspot

Be able to explain what happens along each type of plate boundary and use examples

• Convergent Boundaries: Uses compressional stress to form volcanic island arcs and fold mountains as well as lead to earthquakes and volcanoes

• Divergent Boundaries: Uses tensional stress to form mid-ocean ridges, rift-valleys, and fault-block mountains

• Transform Boundaries: Uses shear stress along faults which can lead to earthquakes

Explain how the Hawaiian Islands were formed by a hot spot

The Pacific Plate moves over the hot spot as magma erupts and cools to form a volcano. As the plate moves, a chain of volcanic islands is formed. Hawaii is the youngest major island in the chain

Explain why the different types of lava result in different types of volcanoes

• Felsic Lava → Cooler, thicker lava that traps gas, building pressure that causes explosive eruptions that build lava domes

• Mafic Lava → Hotter, runnier lava that allows gas to escape easily, causing gentler eruptions that build shield volcanoes

• Intermediate Lava → Can flow or erupt explosively, building composite volcanoes (a.k.a. stratovolcanoes) from layers of lava flows and erupted material

How were the BC mountains formed?

Two tectonic plates collided, magma formed intrusive rock beneath Earth's surface, and glacial ice sheets later eroded and sculpted parts of the mountains.