About 7,700 years ago, a cataclysmic eruption of Mt. Mazama
occurred, forming what is now Crater Lake. This eruption caused
avalanches of pumice and other volcanic rocks to race down the
slopes and flood the valley with deposits over 100 feet deep.
Today, the Pumice Desert is a reminder of what happened so many
years ago. Located north of Crater Lake, the desert is largely
devoid of plants but filled with fields of pumice deposits.
The Pumice Desert is made up of mostly pumice and scoria.
Pumice can be distinguished by its light color, porosity, and
light weight. Pumice is a textural term for a volcanic rock that is
a solidified foam composed of highly microvesicular glass
pyroclastic with very thin, translucent bubble walls extrusive
igneous rock. It is commonly, but not exclusively of silicic or
felsic to intermediate in composition (e.g. rhyolitic, dacitic,
andesite, pantellerite, phonolite, trachyte), but occurrences of
basaltic and other compositions are known. Pumice is commonly pale
in colour, ranging from white, cream or grey, but can be green
brown or black. It forms when gases exsolving from viscous magma
nucleate bubbles which cannot readily decouple from the viscous
magma prior to chilling to glass. Pumice is a common product of
explovie eruptions (plinian and ignimbrite-forming) and commonly
forms zones in upper parts of silicic lavas. Pumice has an average
porosity of 90%, and initially floats on water.
Scoria is usually reddish, darker and heavier than the pumice
fragments. Scoria differs from pumice in being denser, with larger
vesicles and thicker vesicle walls; it sinks rapidly. The
difference is the result of the lower viscosity of the magma that
formed scoria.
Informational sign in the parking area:
References:
http://www2.nature.nps.gov/geology/parks/crla/
http://en.wikipedia.org/wiki/Crater_Lake_National_Park
http://www.virtuar.com/click/2005/crater_lake/
http://en.wikipedia.org/wiki/Pumice
Permission for this Earthcache was granted by the Crater Lake
National Park because of Earthcaches Leave-No-Trace principles, and
the fact there is no placement of a physical cache container. The
placement of any type of cache container is prohibited anywhere
within the Park.
Per the National Park Service:
Please respect the natural beauty and significance of the area. All
vehicles must stay on established and designated roads and parking
areas - and this law is strictly enforced to protect the Pumice
Desert.
In order to log this cache:
1. Go to the following coordinates. It is in a parking area
which will give you a view of the Pumice Desert. Nearby is an
informational sign (See the third photo). Email me what coin can be
seen on the sign.
2. Why is this pumice desert largely devoid of plants? Email me
your theory.
3. Please take a picture of your group at the Pumice Desert and
post it to the gallery. (Optional: I realize not everyone has a
camera with them while geocaching)
4. Email me the number of people in your group.
