Glaciers

Quiz

Percentage of Earth’s surface covered by glaciers today

10%

But, much more extensive in the geologic past

Why are glaciers important

• Spectacular landforms

• preserve information about the atmosphere– in bubbles

• Record evidence of climate change

What is a glacier???

• Thick mass of ice and snow

• shows evidence of movement

• originates on land from– compaction and recrystallization of snow

• forms where snow accumulation in winter exceeds summer melt

• long lasting

Long lasting? Ok, how long???

Remember the hydrologic cycle

Constant motion of water

Ocean atmosphere continent

High elevationHigh latitude

if

Can be thousands of years

Examples of old ice

• Greenland Ice Sheet– greater than 25,000 years olf

• Antarctic – greater than 100,000 years old

– show overhead

Types of glaciers

• Two types– Alpine glaciers

– Continental glaciers

Alpine Glaciers

• Mountain glaciers• Generally confined to mountain valleys

• Examples– Alps– Rockies– Iceland– Kimlamanjaro

Continental Glaciers

• Ice sheets

• massive, thick plates of glacial ice covering an extensive area

• examples– Greenland– Antarctica

Speaking of global warming

• How much do you think sea level would rise if the Greenland and the Antarctic ice sheets were to melt?

50 - 60 meters

How do glaciers move

• Under construction

• show the overhead

How does snow turn into glacier ice?

• Burial and compaction drives off the air

• snow = 90% air– with compaction some of the air is driven off

forming

• Firn (0.4 gm/cc)– with further burial firm is transformed into

• Glacier ice (0.8 gm/cc)

Glacier advance and retreat

• Glaciers are always moving downslope

• However, sometimes they appear to be – advancing– stationary, or– retreating

• How does this work……………………….

To understand glacier advance and retreat we need to understand

Mass Balance

Mass Balance• Zone of accumulation

– where glacier gains mass• ice

• snow

• Zone of accumulation– where mass is lost by

• evaporation

• melting

• calving

Show the overhead

Work of glaciers

• Erode

• transport

• deposit

Glacier Erosion

• As transporters of sediment, glaciers have no equal– once the debris is eroded it does not settle out– capable of transporting large blocks of material

Glaciers erode in 2 ways

• Plucking and quarrying– glacier loosens and lifts rock and incorporates it

into the ice• mechanism = ice wedging

• abrasion– sediment laden ice acts like a rasp, grinding the

rock below• glacier flour = pulverized “powder-like” rock

• glacier striations = linear gouges

Erosional features

• Continental glaciers - subdued terrain

• alpine glaciers - sharp, angular, rugged topography. Glaciers accentuate pre-existing irregularities in the topography

Erosional features to be familiar with

• Glacial trough - U-shaped valley• hanging valley• cirque• tarn• fiord• arete• horn• roch mountonee

• Show overhead

• show slides

Glacial deposits

• Drift - general term for all rock and sediment transported and deposited by a glacier

Two Categories

Till Stratified DriftDeposited directly by glacier ice

First carried by a glacier,then transported and deposited by a stream

Landforms composed of till

• Eratics - large boulders

• Moraines - mount or ridge of till deposited by a glacier– lateral, medial, end, ground

• Drumlins - asymmetrical hills of till

Direction of ice movement

• Show slides

• show overhead

Landforms composed of Stratified Drift

• Outwash plains - plain of glacial meltwater sediment, usually with braided streams

• kettle lake - where block of ice is stranded and buried in till or stratified drift.

• Ice contact features– kames - mounts of stratified drift deposited above or

marginally to a glacier

– eskers - sinuous ridges deposited by streams flowing beneath, in, or on glaciers

• Show the overhead

Ice Ages

• Ice Age = time of extensive glaciation

• Pleistocene Epoch or Pleistocene Ice Age– 2.5 million years ago to 10,000 years ago

The Pleistocene

• Not a time of continuous glaciation, but– glacial advances = glacial period– glacial retreat = interglacial– show the overhead

• during the last glacial maximum (18,000 yrs ago)– glaciers covered 30% of Earth’s land area– 95% of Canada

• Alpine glaciers,

• Laurentide Ice Sheet

Other times of extensive glaciation

• 250 million years ago

• 500 million years ago

• 600 million years ago

• 2.3 billion years ago