The Geologic Story of Mount Rainier: A look at the geologic past of one of America's most scenic volcanoesCrandell, Dwight R. (Dwight Raymond)
Science
The Geologic Story of Mount Rainier: A look at the geologic past of one of America's most scenic volcanoes
Crandell, Dwight R. (Dwight Raymond)
Geology -- Washington (State) -- Rainier, Mount; Rainier, Mount (Wash.)
A little more than 15,000 years ago the long glaciers began to shrink
and recede. By 11,000 years ago there was only about as much ice on
Mount Rainier as there has been within the last century. Then, during a
short period of renewed glacier growth, most glaciers expanded short
distances and new ones appeared in cirques from which ice had
disappeared only a short time before. In some of these cirques so much
rock debris was being dislodged from surrounding cliffs by repeated
freeze and thaw that a rock glacier, consisting mostly of rock fragments
bound together by ice, was formed. A trail to the Huckleberry Creek
valley crosses hummocky rock debris left by such a rock glacier in a
cirque on the southeast side of Mount Fremont. A larger rock-glacier
deposit lies about 2 miles north of Sunrise Point in an east-facing
cirque between The Palisades and Hidden Lake (fig. 18).
In other cirques, where the proportion of ice to rock debris was
greater, the glacier transported the debris a short distance forward and
built a terminal moraine. You can see particularly good examples of
moraines formed about 11,000 years ago near Tipsoo Lake, where the pond
southeast of the lake is dammed by a moraine, and at Mystic Lake. The
ice that formed the terminal moraine at Mystic Lake was a tongue of
Carbon Glacier.
In some places the orientation or altitude of the cirque did not permit
enough snow to accumulate to form a glacier but just enough to create a
permanent snowbank. Rock debris that fell from the surrounding cliffs
rolled down these snowbanks and formed low ridges at their toes. Such a
ridge is called a protalus rampart because it is found just in front of
the apron of rock fragments, called talus, that lies beneath cliffs. A
trail at Sunrise Point leads to protalus ramparts along the north side
of Sunrise Ridge.
Public-domain text, read in full here on John Shaqi.
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