Glaciers

What is a glacier?

A large mass of ice that forms on land and moves under its own weight.

What are the two types of glaciers, and how are they different?

Alpine (valley) glaciers: form in mountains, flow down valleys.

Continental glaciers: large ice sheets covering vast areas (like Antarctica or Greenland).

How and where do glaciers form?

In areas where snow accumulation exceeds melting (ablation) over many years; snow compacts into ice.

What is the snow line?

The lowest elevation where snow persists year-round.

What are zones of accumulation?

area where snow and ice are added.

What are zones of ablation?

area where ice is lost (melting, calving, sublimation).

What are the ways glaciers lose mass?

Melting, calving (breaking off of icebergs), sublimation, and evaporation.

What happens when the rate of ablation is greater than the rate of accumulation?

The glacier retreats (ice front moves backward).

What happens when the rate of ablation is less than the rate of accumulation?

The glacier advances (ice front moves forward).

What happens when the rates of ablation and accumulation are equal?

The glacier is stationary (in equilibrium).

Is the glacier advancing, retreating, or stationary when end moraines form?

Stationary—the glacier's terminus stays in one place for a while.

s the glacier advancing, retreating, or stationary when ground moraine forms?

Retreating—as the glacier melts back, it leaves till behind.

What is moraine?

A ridge or layer of till (unsorted glacial debris) deposited by a glacier.

How do medial moraines form?

When two valley glaciers merge and their lateral moraines combine in the center.

What's special about a terminal moraine?

It marks the maximum advance of a glacier.

What is an outwash plain?

A broad, flat area formed by meltwater streams carrying and depositing sediment beyond a glacier.

What do we find on outwash plains (as evidence of glaciers)?

Sorted sediments, braided stream deposits, and glacial meltwater features.

What is glacial till? What does it look like?

Unsorted, unstratified glacial debris (mix of clay, sand, gravel, boulders).

How do kettle lakes form?

From melting of buried ice blocks that leave depressions filled with water.

Which depositional feature left by glaciers can indicate glacier movement direction?

Drumlins (their tapered end points in the direction of flow).

Which erosional feature formed by glaciers can indicate glacier movement direction?

Striations or grooves scratched into bedrock by moving ice.

Where are tarns lakes found?

in cirques (mountain basins left by alpine glaciers).

Where are paternoster lakes found?

series of small lakes in a glacial valley.

Where are kettle lakes found?

in outwash plains or till where ice blocks melted.