It's Really Tuff EarthCache
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This earthcache is an easy drive SE of Bend. There is little shade, and an easy walking path taking you into the dormant volcanic crater. You will want to spend some time here; bring your lunch and absorb the splendor.
Here you will see an example of volcanic activity mixed with water, and will show you the persistent and powerful effects of water. This awesome sight that can be seen miles away, but truly appreciated only by standing in the crater.
Fort Rock is a prime example of volcanic activity in the Oregon Outback. It was created when basalt magma rose toward the surface and encountered the wet muds of a pluvial (rainwater-sourced) lake bottom. This lake, reaching depths of over 200’, covered most of the Fort Rock and Christmas Valleys, an area between 900 and 1400 square miles.
The combination of hot magma and the wet lake-bottom created an explosive jet of steam, blowing molten basalt into the air. This fountain of hot lava particles and frothy ash flung itself high into the air, with the pieces and blobs of hot lava and ash then raining back down around the vent and forming a saucer-shaped ring of volcanic ash sitting like an island in the lake waters. As a result of heat and pressure, this ring gradually hardened to its current brick-like form. Inside the ring of tuff, trapped waters made up a lake within a lake.
The prevailing southwest winds blew across the broad expanse of surrounding water, beating the waves against the external walls of the ring. In time, the wall on that side of the ring was worn down, opening the crater and allowing the trapped water to escape the rocky ring.
As long as the lake waters surrounded the tuff ring, waves buffetted the outer walls, marking them with wave terraces that show current visitors the evidences of the receding water levels. As climate changed through the centuries, the lake evaporated, leaving the high desert as we find it today.
The level of the crater floor inside the ring was much the same as it had originally been, earning the new formation the definition of a Tuff Ring. A Maar would be formed in the same manner, but the resulting crater floor would be lower than the original ground level. Hole-in-the-Ground is an example of this. Table Rock, another geologic feature in this Outback, is classified as a Tuff Cone, which really is a Tuff Ring on steroids (higher palisade-like sides). All three features, the maar, tuff ring and tuff cone result from volcanic activity mixed with water, either abundant ground or surface water. The same volcanic activity, minus the water, will produce cinder cones or lava flow.
To claim this cache, these requirements must be met:
1. Examine the outer walls carefully, looking for wave terraces formed by the pounding waves of the lake.
a. Email us the number of major water levels you note, evidenced by the wave terraces. Do not include this in your log—the log will be deleted.
2. Post a photo including your group, your GPS and enough of Ft.Rock to be recognizable.
3. Email us the name of the person who donated the land to the State of Oregon for this park. (Same song, 3rd verse)
Additional Hints
(Decrypt)
Fghql gur jnyyf naq gur fvtaf
Treasures
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