Geoscience Reference
In-Depth Information
eight
Ice Returns
the neoglaciation
We are living in an epoch of renewed but moderate glaciation—a
“little ice age” that already has lasted about 4,000 years.
François Matthes,
Report of
Committee on Glaciers
The warm, dry conditions of the mid-Holocene gradually gave way to a
cooler, wetter period known as the “Neoglaciation.” It had no clearly demar-
cated beginning, settling unevenly over the Northern Hemisphere with
considerable local variation. In Europe, notably in southern Norway and in
the Swiss and Austrian Alps, the onset of this cooler period occurred 5,000
to 4,000 years ago, based on the dating of glacial moraines and of sediments
that were eroded by glaciers and transported by glacial meltwaters. Glacial
expansion across Iceland, beginning 5,000 years ago, and the retreat of the
Eurasian tree line between 4,000 and 3,000 years ago also signaled cooler
temperatures.
In the mountain ranges of the American West, many cooler summers
passed without melting the previous winter's snow accumulation. At a
pace of tens of feet per year, glaciers in the high mountain ranges of the West,
from Alaska to western Canada and into the Cascades, Sierra Nevada, and
Rockies, grew and l owed downslope, and the tree line migrated to lower
elevations.
h is period of Northern Hemisphere cooling also brought wetter condi-
tions to the American West. Lakes formed in unlikely places, including some
of the driest places in the West today, such as the Mojave Desert of south-
eastern California. When researchers cored into the dry Mojave lakebeds,
or playas, they were surprised to i nd evidence that large ephemeral lakes,
including Silver Lake today, had formed there 3,620 years ago. In nearby
Searles Basin, playa lakes formed about 3,590 years ago.
