Glaciers
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Glaciers. Dr. R. B. Schultz. Glaciers Glacier -- mass of ice formed by the recrystallization of snow under its own weight (compacted snow becomes “ firn ”). Ice and snow in layers is necessary for development.

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Glaciers

Glaciers

Dr. R. B. Schultz


Glaciers

Glaciers

Glacier -- mass of ice formed by the recrystallization of snow under its own weight (compacted snow becomes “firn”). Ice and snow in layers is necessary for development.

One last requirement: more snow has to be present than melted in the previous year's worth of snowfall so that it can accumulate in layers (annual bands).

Where do glaciers form?

  • In areas where precipitation falls as snow; snow must accumulate.

  • In high (polar) latitudes or at High elevations (in mountains) even at the equator

    Development of the Glacial Theory

    1. 1829 - Swiss engineer named J. Venetz first proposed that glaciers had once been more extensive than at present. His observations inspired Jean de Charpentier to begin a field study of active glaciers.

    2. 1837 - de Charpentier presented his results to the Swiss naturalist, Louis Agassiz (considered to be the "Father of Glaciation"), who developed the first comprehensive theory of glaciation. Based on Uniformitarianism concepts.

    We now know there were several ice ages in Earth history.


Glaciers

Current Glaciers on Earth

Greenland Ice Sheet

Antarctic Ice Sheet


Glaciers

Types of glaciers

1. Ice sheets (continental glaciers) -- cover large areas of land

2. Valley (alpine) glaciers -- form at mountain tops and flow down valleys

How do glaciers move?

Glaciers must be thick enough so that they flow downslope.

Flow is by basal slip or plastic flow.

Basal slip -- ice moves over a thin layer of meltwater

Plastic flow -- ice deforms internally and flows like plastic

Valley (Alpine) Glaciation

Glacial Erosion

Valley (alpine) glaciers erode material at the surface by breaking off pieces of rock and/or by abrasion of underlying rock.

Landforms produced by valley (alpine) glacier erosion

U-shaped valleys

Horns

Cirques

Arêtes

Hanging valleys

Glacial lakes (Tarns)

Groups of glacial lakes: Paternoster lakes


Glaciers

  • Important Stages of Alpine Glaciation

  • Unglaciated v-shaped stream valley

  • Glaciation Stage

  • a. Horn

  • b. Cirque

  • c. Arête

  • d. Medial moraine

  • 3. Post-Glaciation

  • a. Hanging valley

  • b. Pater noster lake

  • c. Tarn

  • d. Glacial trough


Glaciers

Alpine Glaciation Features


Glaciers

Agassiz's Glacial Theory


Glaciers

Proof of Agassiz’s Glacial Theory


Glaciers

Continental Glaciation

Glacial Deposits

Drift -- general term applied to any deposit associated with glaciers

Till -- sediment deposited directly from melting ice; till is unsorted and unstratified

Stratified drift -- deposits from glacial meltwater streams

Outwash -- another term for sediment deposited by meltwater streams

These deposits are stratified and sorted.

Landforms made of till

Moraines -- ridges made of till that form at margins of a glacier

End (or Terminal) moraine -- forms at bottom end of glacier

Lateral moraine -- forms at side of glacier

Ground moraine -- forms by deposition of till at the base of a glacier; not a ridge, just a lumpy plain.

Medial Moraine – when two glacial valleys merge

Drumlins -- streamlined hills made of till; steeper on the side from which ice came The area (south of L. Ontario) is covered by classic drumlin fields.

Landforms made of stratified drift: Kames

Kames -- small, steep-sided hills or mounds.

Kamedeltas -- form where sediments are deposited in meltwater lake

Kame terraces -- form from stratified drift deposited in meltwater streams alongside valley glaciers.

Eskers are sinuous ridges made of stratified drift. The stratified drift is deposited in sub glacial meltwater streams.


Glaciers

Continental Glaciation Landform Features

Southernmost extent of continental glacier


Glaciers

Pleistocene Ice Ages

Pleistocene – “Ice Age” period of geologic time between ~1.7 million and 10,700 years ago.

There have been numerous ice ages during the past 2 million years.

During the Pleistocene ice ages, continental ice sheets covered large areas of land on the North American continent.

Between the ice ages were interglacial periods, warmer periods like we are experiencing now.

Climates were wetter in the early parts of ice ages. Many large lakes formed in the interior of North America

Effects of Pleistocene Ice Ages -- Sea Level Changes

  • During ice ages, sea level fell as water was frozen in Polar Regions.

  • Rivers eroded down to lowered base level.

  • Had many canyons along coastal areas.

  • When sea level rose, river valleys were flooded, forming estuaries like Chesapeake Bay

    Ice ages occurred during the Precambrian, Paleozoic, Mesozoic and Cenozoic.


Glaciers

Pleistocene Glaciation


Glaciers

Pleistocene Glacial Stages in North America:

Recent (15,000 BP) interglacial

Wisconsinan (180,000 BP)

Sangamon (400,000 BP) interglacial

Illinoisan (550,000 BP)

Yarmouth (900,000 BP) interglacial

Kansan (1,400,000 BP)

Aftonian (1,700,000 BP) interglacial

Nebraskan (2,000,000 BP)

Note: State names are glacial advances…local terms are glacial retreats.

Cooling of the Earth

1. Evidence of a decrease in global temperatures of about 8oC during the Cenozoic.

2. Mountain building/tectonics. Rising landmasses acted as wind/moisture barriers.

3. Volcanic dust as a reflector: evidence is weak

4. Decrease in solar radiation: evidence weak despite small variations such as the Little Ice Age between 1450 and 1850.

5. Latitudinal changes in continents: plate tectonics


Glaciers

Cyclic fluctuations in climate

1. Microplankton and 18O (oxygen isotope) record of foraminifer (microfossil) skeletons record temperatures change and thus changes in the ice mass. The data correlate with benthic foram data.

2. A total of 18 glacial expansions during the Pleistocene is known, with a periodicity of +/-100,000 yr.

There are cycles that have been recognized:

“Milankovitch Cycles” (named after Russian scientist, Milutin Milankovitch, who discovered it):

a. 92,500 yr cycle of orbit change from circular to elliptical = deep sea 18O (oxygen isotope) data

b.Precession of the equinoxes due to gravitational attraction by the sun and the moon = wobble in the Earth's spin axis = 22,000 yr

c. Periodic change in the tilt of the Earths rotational axis from 21.8o to 24.4o over a cycle of 40,000 yr.

4. Ultimate cause is probably a combination of plate tectonics and Milankovitch cycles.

Recently, other workers (based on periodic cycles in the rock record) have discovered more cycles.


Glaciers

  • Milankovitch' s Orbital Theory

  • Orbital eccentricities

  • Axis tilt

  • Precession (wobble)


Key terminology

Key Terminology

GlacierFirn

Louis AgassizIce sheet

Continental glaciationValley glacier

Alpine glacierBasal slip

Plastic flowU-shaped valley

HornCirque

ArêteHanging valley

TarnPater noster lake

Medial moraineGlacial trough

DriftTill

OutwashDrumlin

KameEsker

Kettle lakePleistocene Epoch

Interglacial stageMilankovitch cycles

PrecessionAxis tilt

Orbital eccentricitiesMilutin Milankovitch


Pertinent web sites

Pertinent Web Sites

Arctic Research Consortium

The Arctic Research Consortium of the United States (ARCUS) was formed in 1988 to identify and bring together the distributed human and facilities resources of the Arctic research community—to create a synergy for the Arctic in which each resource, when combined with others, can result in a strength that enables the community to rise to the many challenges facing the Arctic and the United States.

Ask a Geologist

If you have questions, a professional geologist is here to help.

Alpine Glacial Landforms

This site presents basic definitions and examples of common alpine glacial landforms discussed in introductory level university physical geography, geology and earth science courses. Examples are provided as photographs with accompanying topographic maps.

Alpine Glaciation Features

Photographs and explanations of features of alpine glaciation.

Arctic Theme Page (NOAA)

NOAA's Arctic Theme Page provides access to widely distributed Arctic data and information for scientists, students, teachers, academia, managers, decision makers and the general public.

Extinctions, Inc.

Fossils from the Extinctions Fossil Company, a commercial source.

Glacial Links

Several links to Web sites containing glacial information.

Glacial Geology, Journal of

Glacial Geology and Geomorphology is an electronic journal of The British Geomorphological Research Group (BGRG) developed by The Queen's University of Belfast and published by The BGRG. It is a refereed journal with a variety of facilities available to subscribers.

Glacial Geology Photo Gallery

Glacial geology images from the Maine Department of Conservation.

Glacial Landforms

Text and images about how glaciers shape the land from the Geological Survey of Canada.


Glaciers

GLACIER (Rice University)

GLACIER is a Web site all about Antarctica and the part Antarctica plays in our global system of weather and climate and oceans and geology. The site is intended to introduce you to the Antarctic and the brave souls who are investigating that vast, frozen continent.

Glacier Bay (NASA)

An excellent NASA site featuring a multi-media tour of Glacier Bay, Alaska.

Glacier National Park—A Virtual Field Trip

This Web site addresses various aspects of alpine glacial landscape interpretation, including landform identification, geomorphic processes, and glacial history. Glacier National Park, Montana, USA, provides the backdrop for this virtual field trip.

Glaciers and Climate Change Links (NAGT)

An extensive listing of glacier and climate change links arranged by topic from the National Association of Geology Teachers (NAGT).

Glaciers and Ice Ages Links (Houghton Mifflin)

Links to several glacier and Ice Ages sites, including class lecture notes, arranged by topic.

Glaciers Links

This Central Michigan University site maintained by Dr. Mark Francek lists several good links to websites containing information relative to topics discussed in the chapter.

Glaciers: Satellite Images

The United States Geological survey (USGS) satellite image atlas of glaciers of the world.

Ice Age Atlas

An atlas of the Ice Age Earth.

Ice Age Exhibit

The Ice Age Exhibit from the Illinois State Museum is an excellent source for Ice Age information.


Glaciers

Ice Age—National Scenic Trail, Wisconsin

A good introduction to Wisconsin's glacial landscape.

Institute For Ice Age Studies

The home page of The Institute for Ice Age Studies (IIAS), an anthropolgy site specializing in the Ice Age.

Landform Atlas of the United States

The color landform atlas of the United States includes shaded relief maps and satellite image maps of each state.

Mendenhall Glacier—A Virtual Tour

Midwestern U.S. 16,000 Years Ago

An exhibit from the Illinois State Museum featuring the midwestern United States 16,000 years ago.

National Geophysical Data Center

The National Geophysical Data Center (NGDC) manages environmental data in the fields of marine geology and geophysics, paleoclimatology, solar-terrestrial physics, solid earth geophysics, and glaciology (snow and ice).

National Parks: Alaska

Links to national parks, national monuments, etc.

National Parks: Washington

Links to national parks, national monuments, etc.

National Snow and Ice Data Center (NSIDC)

The National Snow and Ice Data Center (NSIDC) is a data and information resource for those studying snow and ice, and their importance to the Earth system.

Paleoclimatology Program (NOAA)

Access to a wealth of paleoclimatic data from the National Oceanic and Atmospheric Administration (NOAA).


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