glacial landforms and types

8/10/2019 Glacial Landforms and Types

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Visualizing Physical Geography

Copyright 2008 John Wiley and Sons Publishers Inc.

Chapter 14

Glacial Landforms and the Ice Age

Visualizing Physical Geographyby Alan Strahler and Zeeya Merali


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Chapter

Overview

Glaciers

Alpine Glaciers

Ice Sheets andSea Ice

The Ice Age


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Glaciers

Glacier:large natural accumulation of land ice affected by

present or past flowage

Glacial ice has shaped many landforms in middle and high latitudes Glacial ice sheets affect global climate

Glaciers reflect sunlight

Glacial ice affects global heat transport

Volume of glacial ice affects sea levels

Large bodies of ice are plastic because of

pressure on ice at bottom of massLarge body of ice can flow in response

to gravity

Ice on a slope can slide downwards

Ice sheet:large thick plate of

glacial ice moving outward in all

directions


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Glaciers

Glacial ice builds up when snowfall in winter exceeds

snow melted in summer Each annual layer of snow, melts, refreezes, forms ice

Weight of ice compresses the lower layers into hard crystalline ice

When the ice mass becomes thick enough, the lower layers flow

plastically

Glacial ice forms where temperatures are low and snowfall is high

Alpine glacier: long,

narrow mountain glacier

occupying the floor of atrough-like valley


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Glaciers

Glaciers contain rock of all sizes Glaciers and ice sheets erode and

deposit great quantities of sediment

Glacial abrasion:rock fragments in a

glacier scrape and grind the bedrock

Plucking:moving ice plucks loosened

rock material and carries it away

Sediment is carried, then deposited when

the ice melts


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Alpine Glaciers

Upper part of the glacier is brittle

Lower part is plastic

Zone of accumulation: glacier is

growing Zone of ablation: glacier is

evaporating/melting

Alpine glacier can slide downhill on

meltwater and mud

Rate of movement: few

centimeters/day to several meters/day

Surge: rapid movement of alpine

glacier, up to 60 m/day for several

months


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Alpine Glaciers

Landforms Made by Alpine Glaciers


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Alpine Glaciers



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Alpine Glaciers

Landforms Made by Alpine Glaciers Cirque:valley head enlarged and hollowed out

by glaciers, producing bowl-shaped valley

Arte:sharp ridge formed between two cirques Horn:steep-sided peak formed by glacial

erosion from three sides

Col:natural pass or low notch in an arte

between opposed cirques

Moraine:accumulation of rock debris carried by

an alpine glacier and deposited by the ice tobecome a depositional landform

Tarn:small lake occupying a rock basin in a

cirque

Hanging valley:stream valley that has been

truncated by glacial erosion so as to appear in

cross section in the upper wall of a glacial

trough


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Alpine Glaciers



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Alpine Glaciers


Glacial trough:deep, steep-

sided rock trench formed by

alpine glacier erosion

Fiord:narrow, deep ocean inlet

partially filling a glacial trough


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Ice Sheets and Sea Ice

Ice Sheets of the Present

Antarctic Ice Sheet

13 million sq km

4000 m thick

Greenland Ice Sheet

1.7 million sq km

3000 m thick


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Sea Ice and Icebergs

Sea Ice:floating ice of the oceansformed by direct freezing of

ocean water

Always


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Sea Ice and Icebergs

Iceberg: mass of glacial ice floating

in the ocean that has broken off aglacier that extends into tidal water

May be hundreds of meters thick

About 5/6 of the iceberg is submerged

Always fresh water


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Landforms Made by Ice Sheets

Ice sheets scrape off regolith and abrade bedrock

Grooves, scratches, and polished rock show evidence of ice sheets

I Sh t d S I


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Ice sheets pick up rock fragments,

transport them, and deposit themwhen the ice evaporates or melts

Glacial drift:general term for all varieties

and forms of rock debris deposited by ice

sheets

Stratified drift:layers of sorted clays, silts,sands or gravels, deposited by meltwater

streams or lakes

Till:unstratified mixture of rock fragments

of all sizes, deposited directly by the ice

Ground moraine:thin, even cover of till

I Sh t d S I


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Esker:narrow, often sinuous

embankment of coarse gravel andboulders deposited in the bed of a

meltwater stream in a tunnel

within stagnant ice in an ice sheet

Drumlin:smoothly rounded, oval

hills of glacial till, formed by the

moving ice

Terminal Moraine:glacial till that

accumulates at the farthest

advance of the ice sheet

I Sh t d S I


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Moraine:accumulation of rock

debris carried by an ice sheetand deposited by ice to become

a depositional landform

Outwash Plain:formed from

stratified drift left by streams

issuing from the ice

I Sh t d S I


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Recessional Moraine:moraine

formed when the ice paused in its

retreat

Kame:steep-sided mound of

stratified sand and gravel

deposited at or near the terminus

of a glacier

I Sh t d S I


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Pluvial Lakes: lakes formed during a moister climate, during the iceages

Many pluvial lakes formed in the western U.S.

Lake Bonneville, in western Utah, was about the size of Lake Michigan

Pluvial lakes shrank or dried up as the climate became warmer and drier

Th I A


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The Ice Age

Glaciation: single episode or

time period in which ice sheets

formed, spread, and

disappearedGlaciation occurs when

temperatures drop or snowfall

increases

There have been many

glaciation episodes in Earths

history

55 million years ago

5 million years ago

Recent ice ages

Th I A


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The Ice Age

Late-Cenozoic Ice Age: series of glaciations, deglaciations, and

interglaciations experienced during the late Cenozoic Era

Maximum Glaciation in North

America and Europe

The Ice Age


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The Ice Age

Investigating the Ice Age

Scientists study the glacial history of the Ice Age: Take sediment core samples on the deep ocean floor

Use evidence of magnetic reversals to find the age of the sediments

Study composition and chemistry of the cores

Create a record of dates, temperatures, biology, and chemistry

using the core samples

Deep-sea cores show alternating glaciations and

interglaciations going back 2-3 million years

The Ice Age


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The Ice Age

Possible Causes of the Ice Age

1. Motions of tectonic

plates brought land-mass to high latitudes

2. Volcanic activity

produced dust that

blocks solar radiation

3. Decrease in Suns

energy output

4. Change in atmospheric

composition; reduction

in greenhouse gases

The Ice Age


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The Ice Age

Possible Causes of Glaciation Cycles

Astronomical hypothesis:

explanation for glaciations and

interglaciations based on cyclicvariations in the solar energy

received at the Earths surface

The Ice Age


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The Ice Age

Holocene Environments

Holocene Epoch: last epoch of geologic

time, commencing about 10,000 years

ago and including the present

Three major climate periods in Holocene:

Boreal Stage: boreal forest vegetation in

midlatitude regions

Atlantic Stage: warmer temperatures, about8000 years ago

Subboreal Stage: cooler, about 5000 years

ago to 2000 years ago

During past 2000 years:

Warm from AD 1000 to 1200 Little Ice Age from AD 1450 to 1850

Global temperatures increasing at present

Fossil pollen and spores

preserved in glacial bogs show

changes in vegetation over

time

Ice Sheets and Global Warming


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Disintegration of Larsen B ice shelf, Antarctica, 2002

31 Jan 2002 23 Feb 2002

3 Mar 2002 5 Mar 2002



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Polar sea ice has been decreasing in the last 50 years

glacial landforms and types

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