A Maar'd Hole in the Ground EarthCache
A Maar'd Hole in the Ground
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Difficulty:
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Terrain:
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Size: 
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This Earthcache will take you to a dry maar, a low-relief, broad volcanic crater formed by shallow explosive eruptions. Because of the nature of the volcanic explosion, a maar will frequently be filled with water, such as Battleground Lake, in WA state.
Hole-in-the-Ground did not fill with water after its forming event, thousands of years ago. The volcanic mountain rose at the edge of a huge, pluvial (rain-formed) lake that covered most of the Ft. Rock Basin.
The hot, rising magma turned the ground water into explosive steam, which then blew the top of the mountain into the air. Scientists believe that there were 4 significant explosions during this formation period, which blew rocks up to 8 meters (26’) in size close to 4 miles away. There are numerous large, volcanic rocks that have rolled back into the crater, and scattered about the landscape outside of the crater as well.
“The crater was formed in a few days or weeks by a series of explosions that were triggered when basaltic magma rose along a northwest-trending fissure, or diatreme, and came into contact with abundant ground water at a depth of 300 to 500 m (984’-1640’) below the surface. After the initial explosion, repeated slumping and subsidence along a ring-fault led to intermittent closures of the vent, changes in the supply of ground water, and repeated accumulations of pressure in the pipe.” Heiken, Fisher & Peterson.
The crater is now 367’ to 840’ below the original ground level, which fulfils the requirement to be classified as a maar---the crater floor is lower than original surface.
PLEASE NOTE:
While this location, and the roads leading to it, are on National Forest property, some of the property that surrounds the access roads is private property, and the Forest Service personnel request that, on your drive to this cache, you stay on the posted forest service roadways.
The coordinates will bring you to the western rim of the crater of Hole-in-the-Ground. Your mission, should you choose to accept it, will require you to accomplish these tasks in order to claim the cache:
1. At the posted coordinates, note your elevation on your GPSr. Take a careful drive around the rim track, stopping at the eastern rim. There is room for parking off the track. Make your way to the highest spot (in your determination) and again make note of the elevation.
Email us the difference in elevation between the east and west rims. DO NOT post this in your on-line log. Your post will be deleted.
2. At your stop on the eastern rim, find some of the pebble-sized volcanic rocks.
Email us the color of these pebbles. (ditto the logging note above)
3. Post a photo that shows your caching party, your GPSr, and the crater.
IMPORTANT: The rim track is just over 3 miles long. The track is well-worn, but has assorted rocks that add to the bumpiness of the ride. A low-slung vehicle could find the way too challenging, but any other vehicle should find it passable. Two-wheeled or pedestrian transportation will also work well.
Additional Hints
(Decrypt)
Rawbl gur ivrj!
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
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