Volcanic Ash Earthcache EarthCache
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As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
This earthcache is located a few miles east of Burney, CA. This earthcache can be earned from the comfort of your car (except for the picture). Pull off the highway at the 1-car pullout on the north side of the road.
The products of a volcanic eruption are volcanic gases, lava, steam, and tephra. Magma is blown apart when it interacts violently with volcanic gases and steam. Solid material produced and thrown into the air by such volcanic eruptions is called tephra, regardless of composition or fragment size. If the resulting pieces of ejecta are small enough, the material is called volcanic ash, defined as such particles less than 2 mm in diameter, sand-sized or smaller. These particles are small, pieces of magma and rock that have been tossed into the air by outbursts of steam and other gases.
Strictly speaking, the tuff cliff across the road from where you are speaking is composed of small crystals of rock of igneous origin.
There are different types of tuff cliffs since this tephra (ash) varies in color based on the minerals present in the ash deposits:
Rhyolite cliffs – contain small glassy fragments and non-chrystaline quartz. They are composed of shattered glass (obsidian) rocks. These cliffs often “glint” in the sunlight and often appear white from a distance because the light is being refracted. Under a magnifying glass the rocks are usually black or translucent.
Trachyte cliffs -- contain little or no quartz but much snidine or anorthoclase and sometimes oligoclase feldspar, with occasional biotite, augite and hornblende. In weathering they often change to soft red or yellow clay-stones.
Andesitic cliffs – contain scoria fragments of all sizes from huge boulders to volcanic “flour.” Typically metamorphic action has also worked on the cliffs, leaving secondary elements to fill in the “holes.” These secondary minerals include calcite, chlorite, and quartz to name a few. The original volcanic ash is decomposed (obsidian) glass. In color, the cliffs are red or brown.
Basaltic cliffs -- contain basalt, and other ancient rocks. The cliffs are black, dark green or red in colour; vary greatly in coarseness, some being full of round spongy bombs a foot or more in diameter, and, being often submarine, may contain shale, sandstone, grit and other sedimentary material, and occasionally may contain fossils.
Congrads to Can'tseem for FTF (First to Finish logging requirements)
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile.
1. List the name “GC23G65 Volcanic Ash Earthcache” in the first line of your email. Also, list the number of people in your group.
2. As you look at the ash cliff on the south side of the road, what color do you see? Does the ash appear to vary in size or is it of a uniform and small size? Does it glint in the sunlight? Are there “large spongy bombs” visibly present? Based on your observations, what type of tuff cliff are you looking at?
3. Each layer of ash is presumed to have been deposited by a separate volcanic explosion (look for lines of lighter then darker “sediment”). Does this cliff therefore indicate MANY or FEW volcanic explosions (are there few or many apparent layers)?
4. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Post a picture of yourself and your GPS with your log that shows you and/or your GPSr with the HIGHWAY in the background. Do not show pictures of the cliff since they would give away logging requirements.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Congrads to cantseem for FTF (first to Finish logging requirements) on Feb 7, 2010.
Resources:
Alt & Hyndman, Roadside Geology of Northern andCentral California. Mountain Press Publishing. Missoula: Montana. 2000.
Wikipedia Article “Tuff” (visit link)
Additional Hints
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