Castle Lake is reached by paved road. There is a parking lot that
often gets busy on the weekends. Winter snows may make the
EarthCache inaccessible.
Castle Lake was formed during a Pleistocene glaciation 10,000
years ago. Glaciers leave distinctive geomorphological features.
These features include erratics, u-shaped valleys, chatter marks,
moraines, 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 glacier
ice to form and start flowing. Flow in this kind of glacier is down
the back side 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
side walls often collapse since they are no longer supported by the
glacial ice. And 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, send me a note with :
- The text "GC231WX Castle 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 (if you can get
there?)
- What direction is the headwall?
- Have the headwall and sidewalls collapsed after the support of
the glacier melted?
The following sources were used to generate this
cache:
- Castle Lake Geography; Copyright © 2008
Castle Lake Limnological Research Station;
http://castlelake.ucdavis.edu/geography/castle_lake
- 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