South
Lake is reached by a moderate to strenuous hike into the Dinkey
Lakes Wilderness. It is approximately 3 miles from the parking area
and at an elevation of about 9300 feet. The parking area is
accessible by unpaved Forest Service access roads. The roads do get
pretty rough, so a high clearance vehicle would be a very good
idea. Winter snows make the EarthCache inaccessible.
The Sierra Nevada Mountains have been repeatedly covered with
glaciers over the past 1.5 million years. Due to the erosive nature
of glaciers, each glaciation that is larger than the previous ones
plows over the older landforms and erases the evidence of prior
smaller less extensive glaciations. As a result the timing and
number of glaciation events is constantly under debate.
However, some glaciations have been either extensive or lasted
long enough to have left evidence of their occurrence. The Sherwin
Glaciation, which occurred about 1 million years ago, is one of
these major glaciations. The two most recent events are called the
Tahoe and Tioga glaciations. The Tahoe glaciation is thought to
have occurred in two stages between 200 and 140 thousand years ago
and from 50 to 42 thousand years ago. The Tioga glaciation is more
recent, occurring between 25 and 14 thousand years ago. Of the two
recent glaciation events, the Tioga glaciation is thought to be
just a little less extensive than the Tahoe.
Glaciers leave distinctive geomorphologic features. These
features include erratics, u-shaped valleys, moraines, chatter
marks, striations, and cirques.
Cirques form at the head of a glacier, often on the northern
slopes of mountain ranges. It begins with a preexisting depression
that fills with snow and ice. That snow and ice gradually pry off
pieces of rock from the base and sides of the depression gradually
making it deeper. As the depression gets deeper, the snow and ice
remain in shadow longer allowing glacial ice to form and start
flowing.
Flow in this kind of glacier is down the backside of the
depression, along the floor then out. The movement of the glacier
speeds up the erosion on the sides and floor of the depression,
creating an increasingly deep and sheer walled depression. After
the glacier melts, portions of the seep sidewalls often collapse
since they are no longer supported by the glacial ice. The
depression often fills with water forming a lake that is called a
tarn.
Three main characteristics are used to identify a cirque:
- A steep headwall and sides
- A deep basin
- A low ridge of bedrock or moraine on the 4th side
Logging requirements:
- The text "GC30XP8 South Lake – A Cirque" on the first
line.
- The number of people in your group (put in the log as
well).
- What part of a cirque are the coordinates.
- What direction is the headwall?
- Have the headwall and sidewalls collapsed after the support of
the glacier melted? ?
The above information was compiled from the
following sources:
- Extent of Glaciation, Sierra Nevada Photos;
http://www.sierranevadaphotos.com/geography/glaciation.asp
referring to Atlas of California, 1979. Glaciers of California,
Guyton, 1998
- Garry Hayes, Glaciation of the Sierra Nevada;
http://virtual.yosemite.cc.ca.us/ghayes/sierragla.htm
- BSG 1996-2008; last modified: 14th Sep 2009;
Glacial Erosion Landforms (Large¬scale);
http://www.geomorphology.org.uk/pages/education/alevel/coldenvirons/Lesson
%2011.htm
- Corrie or Cirque Formation;
http://www.fettes.com/cairngorms/corrie%20formation.htm
.