Napa Valley Ice Cubes – Earthcache EarthCache
Napa Valley Ice Cubes – Earthcache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
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 found on Hwy 29 between Calistoga and Middletown. There is a wide pullout with a great view of Napa Valley to the west and the Pallisades outcrops to the east. You are looking east at Mt. St. Helena to the east to fulfill the requirements.
If you have completed any of the region’s “Sonoma Volcanics” earthcaches, you are already aware that the mountains surrounding Napa Valley were formed from a now-extinct volcanic series of actions.
The focus of this earthcache is a unique form of the basalt flow -- Columnar basalt.
Geology:
Columnar basalt -- During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The result of this rapid cooling is what you see before you. Another way to understand this is to think of the “reverse” of ice formation as ice cubes in a freezer tray. When one fills ice cube trays with water, if one fills the trays “all the way to the top” when one examines the formed ice cubes a few hours later, the cubes have OUTGROWN their container, yet for the most part (depending on the rapidity of the freezing) maintained the “cube” shape. The natural “fracture shape” of basalt is cubical. That means that if the “freezing” action takes place rapidly enough, then the cubical “column structure” forms. And herein lies a challenge. If the basalt is cooling super-slowly then no columns form; however, if the basalt cools too quickly, then the columns are miniscule and can be seen only in close structural observation. Therefore, a “medium-fast” level of cooling is needed.
Perhaps the most famous basalt flow in the world is the Giant's Causeway on the northern coast of Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed. Other famous basalt columns include:
• Cape Stolbchatiy, Kuril Islands, Russia
• Devil's Postpile, California
• Devil's Tower, Devils Tower National Monument, Wyoming
• Organ Pipes National Park, Victoria, Australia
• Prismas Basálticos in Hidalgo, Mexico
Congrads to luvbassn and luvbassn2 for co-FTF.
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile.
1. List the name “GC23J5Y Napa Valley Ice Cubes Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Estimate the % height of the columns of the Mt. St. Helena Geologic column. Also, where in the layering (top, middle, bottom) is this basalt column?
3. From the information above is basalt column formation caused by:
a. Igneous volcanic action
b. Sedimentary action
c. Metamorphic action
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/or your GPS with your log that shows Mt. St. Helena behind you.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Resources:
Alt & Hyndman, Roadside Geology of Northern andCentral California. Mountain Press Publishing. Missoula: Montana. 2000.
Geology.about.com -- (visit link)
Wikipedia – columnar basalt
Additional Hints
(No hints available.)