The Southern Patagonian Icefield
of Argentina and Chile is the southern remnant of the Patagonia Ice
Sheet that covered the southern Andes Mountains during the last ice
age. This detailed astronaut photograph illustrates the terminus of one
of the icefield’s many spectacular glaciers—Upsala Glacier, located on
the eastern side of the icefield. Upsala is the third largest glacier
in the icefield, and like most other glaciers in the region, it has
experienced significant retreat over the past century.
This image was taken during spring in the Southern Hemisphere, and
icebergs were calving from the glacier terminus into the waters of Lago
Argentino (Lake Argentina, image right). Two icebergs are especially
interesting because they retain fragments of the moraine (rock debris)
that forms a dark line along the upper surface of the glacier. The
inclusion of the moraine illustrates how land-based rocks and sediment
may wind up in ocean sediments far from shore.
Moraines are formed from rock and soil debris that accumulate along
the front and sides of a flowing glacier. The glacier is like a
bulldozer that pushes soil and rock in front of it, leaving debris on
either side. When two glaciers merge (image center), moraines along
their edges can join to form a medial moraine that is drawn out along the upper surface of the new glacier.
The moraine can be carried intact to the terminus and included in
icebergs that then float away, dropping the coarse debris as the
iceberg melts. While the icebergs produced by Upsala Glacier do not
reach an ocean, many current glaciers do. The existence of ancient
glaciers and ice sheets is recorded by layers or pockets of coarse,
land-derived sediments within finer-grained sea floor sediments that
are located far from any current (or former) coastline.
Astronaut photograph ISS021-E-15243
was acquired on October 25, 2009, with a Nikon D2Xs digital camera
fitted with a 400 mm lens, and is provided by the ISS Crew Earth
Observations experiment and Image Science & Analysis Laboratory,
Johnson Space Center. The image was taken by the Expedition 21 crew. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program
supports the laboratory to help astronauts take pictures of Earth that
will be of the greatest value to scientists and the public, and to make
those images freely available on the Internet. Additional images taken
by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, NASA-JSC.