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| Ice Age Cook Inlet |
Lowland Periglacial Landscapes
Ice Age Cook Inlet: Over the past three-quarters
of a million years, there have been 8 major ice
ages. During the most extreme phase of at least
some of those ice ages, this part of Alaska was
buried in ice, perhaps hundreds of yards/ meters
thick. During more moderate phases, most of the
ice has concentrated around mountain peaks and
valleys, and in the valleys leading out of mountains
-- including Cook Inlet, as simulated at right.
Recall that sea level was roughly 100 yards/meters
lower during some Ice Age extremes. Cook Inlet
was correspondingly deeper before sediment from
glaciers gradually filled it. What remains is laced
with treacherous shallows where many ship has run
aground, especially during low tide. The difference
in depth between low vs. high tides can exceed 7
yards (6 m).
of a million years, there have been 8 major ice
ages. During the most extreme phase of at least
some of those ice ages, this part of Alaska was
buried in ice, perhaps hundreds of yards/ meters
thick. During more moderate phases, most of the
ice has concentrated around mountain peaks and
valleys, and in the valleys leading out of mountains
-- including Cook Inlet, as simulated at right.
Recall that sea level was roughly 100 yards/meters
lower during some Ice Age extremes. Cook Inlet
was correspondingly deeper before sediment from
glaciers gradually filled it. What remains is laced
with treacherous shallows where many ship has run
aground, especially during low tide. The difference
in depth between low vs. high tides can exceed 7
yards (6 m).
Cook Inlet currently.
of both the Susitna and Turnagain
Arms of Cook Inlet. Just north of the
juncture of those two Arms is the site
where Anchorage now rests.
Arms of Cook Inlet. Just north of the
juncture of those two Arms is the site
where Anchorage now rests.
Although these photos at right and
below are of other glacial valleys
during the 20th century, they provide a
rough idea of what Cook Inlet looked
like in thousands of years ago.
below are of other glacial valleys
during the 20th century, they provide a
rough idea of what Cook Inlet looked
like in thousands of years ago.
that glacial left a huge terminal
moraine running east to west across
the Inlet. As the glacier retreated, that
terminal moraine served as a dam,
trapping water from the melting
glacier, and forming a huge
freshwater lake.
moraine running east to west across
the Inlet. As the glacier retreated, that
terminal moraine served as a dam,
trapping water from the melting
glacier, and forming a huge
freshwater lake.
As the lake's depth increased, water pressure
against the dam increased too, until eventually it
burst, and all that fresh water was flushed out to
sea.
Left behind are remnants of the dam, and thus of
the terminal moraine, in the form of what are
known as the East and West Forelands. This is
the narrowest part of the Inlet southwest of
Anchorage.
Bedrock on both sides of the Inlet is covered with
a thick layer of glacial till -- some of it left by the
massive glaciers that once covered those lands,
and the rest of it eroded by glaciers in the
flanking mountains and carried downstream by
rivers flowing out of the glaciers. The Kenai
River was one of the largest. Anywhere that you
dig into the ground on the Kenai Peninsula, you
are likely to run into a combination of sand,
gravel, and cobbles, some much larger than a
softball. Here and there are also boulders (i.e.,
erratics) some the size of a modest house.
against the dam increased too, until eventually it
burst, and all that fresh water was flushed out to
sea.
Left behind are remnants of the dam, and thus of
the terminal moraine, in the form of what are
known as the East and West Forelands. This is
the narrowest part of the Inlet southwest of
Anchorage.
Bedrock on both sides of the Inlet is covered with
a thick layer of glacial till -- some of it left by the
massive glaciers that once covered those lands,
and the rest of it eroded by glaciers in the
flanking mountains and carried downstream by
rivers flowing out of the glaciers. The Kenai
River was one of the largest. Anywhere that you
dig into the ground on the Kenai Peninsula, you
are likely to run into a combination of sand,
gravel, and cobbles, some much larger than a
softball. Here and there are also boulders (i.e.,
erratics) some the size of a modest house.
mountains are not the only fascinating features
left behind by glaciers.
left behind by glaciers.
| Bear Viewing Association To watch, to wonder, and to conserve [email protected] Ph/Fax (907) 260-9059 (Office) 39200 Alma Ave. Soldotna, AK 99669 |
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| Bear Viewing Association To watch, to wonder, and to conserve [email protected] Ph/Fax (907) 260-9059 (Office) 39200 Alma Ave. Soldotna, AK 99669 |
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| Glaciers, Glacial Landscapes, and Their Roles in the Ecology of Alaskan Bears |