|
ParkWise >
Teachers > Nature > Glaciers Of Kenai
Fjords
Glaciers Of Kenai Fjords
Background
  
Over the last one billion years, large
parts of the planet were covered by glacial ice that has advanced and shrunk in
cyclic periods. In fact, in the last 1.5 million years, there have been at
least 20 cycles during which Earth's ice sheets have grown to twice the size
they are today and then shrunk back.
Ice sheets are very large glaciers. A
glacier is an accumulation of ice, air, water and rock debris or sediment.
Glaciers are so large that they flow downhill - literally - under the influence
of gravity. Glaciers advance at different rates - some slowly, some quickly.
Scientists don't fully understand why rates differ. Exit Glacier in Kenai
Fjords advances almost two feet per day. Glaciers can be as large as continents
or as small as mountain valleys.
Large or small, glaciers leave abundant
evidence of their presence, even after they have melted and the ice has
disappeared. Glaciers erode the landscape, carving valleys and small lakes,
wearing away rock, and stripping soil from the ground. They also add to the
landscape by depositing materials from huge boulders to piles of rock and other
debris dragged along as the glacier flows downhill.
Kenai Fjords National Park's Exit Glacier
is an active, retreating remnant of a larger glacier once extending to
Resurrection Bay. Here are found newly exposed, scoured, and polished bedrock
and a regime of plant succession - from the earliest pioneer plants to a mature
forest of Sitka spruce and western hemlock.
Exit Glacier is a half-mile wide, dynamic
river of ice whose source is the 250 square mile Harding Icefield. This outlet
glacier flows out of the higher Harding Icefield and down the U-shaped glacial
valley for about three miles, descending approximately 2700 feet to the Exit
Creek outwash plain. The glacier moves forward about two feet per day, carrying
all sizes of rock material plucked from the underlying rock and side walls, as
well as material falling from the valley sides and coming to rest on the
glacier's surface. Rocks embedded in the bottom of the moving ice continually
gouge and grind the underlying base rock to flower-size particles that give
Exit Creek its milky color.
Scientific teams and individuals find Exit
Glacier an excellent "research laboratory" into the mysteries of glaciers. Two
scientists, Joel A. Cusick and Bruce Molnia, Ph.D., are studying changes to the
landscape resulting from glaciation and changes to the park's glaciers as a
result of global warming. The excellent maps and much of the information in
this unit come from their research.
> Unit
Outline >
|
