Environments of Deposition: Glaciers, Deserts, Oceans and Shorelines

Glacier

A mass of ice on land that moves by plastic flow and basal slip

What percentage of the land surface is covered by glaciers?

10

Why are glaciers considered part of the rock cycle?

They transport and deposit sediment

Where is the largest percentage of Earth’s freshwater held?

Glaciers

What are the types of glaciers?

Valley glaciers and continental glaciers

Valley glaciers

A glacier confined to a mountain valley or an interconnected system of mountain valleys

Valley glaciers flow from…

Higher elevations to lower elevations

Valley glaciers flow in…

A pre-existing stream valley

Valley glaciers are…

Relatively small, but they are longer than they are wide, like rivers

Continental glaciers

A glacier that covers a vast area of at least 50,000 km² and is not confined by topography

Continental glaciers are also called…

Ice sheets

Continental glaciers are only found in…

Greenland and Antarctica

Step 1 of forming a glacier

Air infiltrates snow

Step 2 of forming a glacier

Snowflakes become smaller, thicker and more round as air is forced out

Step 3 of forming a glacier

Snow is re-crystalized into a much denser mass of small grains called firn

Step 4 of forming a glacier

Once the thickness of ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals

What is the composition of glacial ice?

90% solid, 10% air

How long can it take for firn to fuse into ice crystals to create glacial ice?

Hundreds of years

Plastic flow

The flow of ice under pressure that causes deformation with no fracturing (internally)

Basal slip

Movement involving a glacier sliding on meltwater over its underlying surface (bedrock)

What behavior does the lower portion of a glacier present?

Analogous to a plastic

What behavior does the upper portion of a glacier present?

Like it is brittle

What are the three mechanisms of glacial erosion?

Plucking, abrasion and bulldozing

Plucking

Glacier moving over fractured rock loosens, picks up pieces and carries them along

Abrasion

Material picked up by plucking, ground up and acts like sandpaper

Striation

A straight scratch caused by the movement of glacial ice

Glacial polish

A smooth glistening rock surface formed by the movement of ice over bedrock

Glacial flour

Very small, silt / mud / clay sized particles that affects the color and consistency of meltwater

Bulldozing

Glaciers shove and push materials in their paths

This is not really a formal geologic term for glacial erosion mechanisms, but applicable and self-explanatory

Bulldozing

What are the types of erosional landforms created by glaciers

U-shaped valley, hanging valley, cirque, arête, horn, fjords

U-shaped valleys

Glaciers flow existing pathways and stream valleys, which erode them into a valley with steep walls and a broad flat floor

U-shaped valleys are also called…

Glacial troughs

Hanging valley

A tributary glacial valley whose floor is at a higher level than that of the main glacial valley

Streams and rivers plunge over vertical or steep cliffs in hanging valleys. What does this create?

Beautiful waterfalls

Cirque

Steep-walled bowl-shaped depression on a mountainside at the upper end of a glacial valley

What are cirques analogous to?

A pond, or a volcano crater

What are cirques usually filled with?

Snow, ice, or meltwater, but they can be empty

Arête

a narrow, serrated ridge between two glacial valleys or adjacent cirques

How are arêtes formed usually?

Erosion in two parallel glacial troughs, reducing the intervening ridge to a thin snipe of rock

Horn

A steep-walled pyramid-shaped peak formed by the headward erosion of at least three cirques

What is the most famous horn?

Matterhorn in Switzerland

Fjords

An arm of the sea extending into a glacial trough eroded down below sea level

When do most fjords form?

During the Pleistocene when sea level was ~ 130m lower than now and glaciers were more extensive

How are fjords made?

The glaciers erode the valleys, then sea level rises and floods

Glacial deposits

refer to all the material eroded and transported by glaciers

What is the general term for “glacial deposits”?

Glacial drift

What are the types of glacial deposits?

Till and stratified till

Till

Unsorted, unstratified sediment deposited directly by a glacier

Stratified till

Sediments deposited that are layered and shows evidence of sorting

What are some uses for stratified till?

Groundwater reservoirs, as well as sand and gravel in construction

Glacial erratics

A rock fragment carried some distance from its source by a glacier and usually deposited on bedrock of a different composition

Erratics can be used to…

Trace the path of old glaciers

How heavy can glacial erratics be?

Up to 7,200 tons

How big can glacial erratics be?

House-sized

Glacial moraines

Long, sinuous hills composed of glacial till material

When a glacier becomes stationary within a valley, there is no forward movement and no retreat. What happens inside the glacier?

Ice still moves within it and sediment is still being deposited

End moraines

The pile of rubble and till material piled up at the forward edge of the glacier

What is another name for “end moraines”?

Terminal moraines

End moraines will continue to form as long as…

The glacier is stationary

What do end moraines look like?

Long, crescent-shaped ridges of till spanning a valley or open plain

Lateral moraines

Ridges of sediment deposited along the margin of a glacier

Medial moraines

Where two lateral moraines merge together, usually when tributary glaciers flow into a larger glacier

Drumlins

An elongate hill of till formed by the movement of a continental glacier or by floods

What do drumlins usually form?

Drumlin fields that contain hundreds of thousands of drumlins

What do drumlins look like?

Steep side and a gently sloping end that points in the direction of ice movement

What are the glacial deposits of stratified till?

Esker, kame and kettle

Esker

A long, sinuous ridge of stratified drift deposited by running water in a tunnel beneath stagnant ice

How big can eskers be?

As high as 100m and as long as 500km

What do eskers look like?

Sharp crests and sides that slope ~ 30°

Kame

Conical hill of stratified drift originally deposited in a depression on a glacier’s surface

Kettle

Depressions in the land which formed due to the melting of large ice blocks off of a glacier

Kettles create a landform known as…

Kame and kettle topography

What are kettles also known as?

Golf courses

Where was golf created?

Scotland, home of kame and kettle topography

What percentage of the land surface was covered by ice during the Pleistocene Ice Age?

Over 30

How long ago did the Pleistocene Ice Age start?

~ 2 - 3 million years ago

How long ago did the Pleistocene Ice Age end?

100,000 years ago

What was formed during the Pleistocene Ice Age?

Beringia (or the “Bering Sea Land Bridge”) between Russia and Alaska

Lake Agassiz

Extremely large glacial lake formed near the end of the Pleistocene

What fed the Lake Agassiz?

Meltwater from the retreating Laurentide Ice Sheet

How big was the Lake Agassiz estimated to be?

~ 440,000 mi²

How long ago was Lake Agassiz’ final draining?

~ 8,200 years ago

Lake Agassiz may have caused…

An expansion in agriculture in Europe due to climate shift from meltwater entering the oceans

Snowball Earth

Large scale glaciation that happened during the Cryogenian

Which of the following statements is supported by current scientific evidence regarding 'Snowball Earth' events?

A) They occurred only once in Earth’s history

B) They happened several times throughout Earth’s history

C) They are purely hypothetical with no supporting evidence

D) They only affected the polar regions

B

Desert

An area of the Earth’s surface where vegetation covers less than 25% of the surface, less than 10 in. of average annual rainfall, and has very high evaporation rates

What are most deserts called?

Low-latitude deserts

Due to wind movements, deserts are areas of…

High pressure and sinking air that is compressed and warmed

What are the main types of deserts?

Subtropical (Tradewinds), rain shadow, coastal, tundra / polar

What is the largest desert?

Antarctica, with ~ 8 in. of rain per year

What atmospheric feature is primarily responsible for the formation of tradewind deserts?

Hadley Cells

What type of desert is the Sahara classified as?

Tradewind desert

In tradewind deserts, what happens to warm, moist air as it rises at the equator?

It cools and expands, dropping rain

What is the effect of the Earth's rotation on Hadley Cell movement called?

Coriolis Effect

What type of desert is Death Valley classified as?

Rain shadow desert

In rain shadow deserts, what happens to warm, moist air when it flows inland from the oceans?

It expands and cools, dropping rain on one side of mountain

In a rain shadow desert, what happens on the side opposite the mountains?

Dry air sinks and evaporates remaining moisture

What causes the air to warm and compress in rain shadow deserts?

The evaporation of any remaining moisture

What atmospheric condition is common in rain shadow deserts?

Warm and dry air