A few years back, L and I stumbled into Devil's Postpile National Monument at the end of a vacation day in California. Neither one of us knew what was there - so we went check it out. We found the most amazing natural structures. "Tiles" seemed to have been perfectly laid out on the ground, in the middle of nowhere!
It turns out that those "tiles" were the ends of 60ft high columnar basalts that had been "polished" by glaciers running over them. You can still see the linear streaks of the glacial polish.
Photos and the text below are from the National Park Service website:
"Approximately 100,000 years ago, a lava flow erupted two miles upstream from the location of today's Monument. As it flowed down the Valley, it eventually ran into an obstruction which served as a dam to the lava's path. Pooling up to as deep as 400 feet behind the natural dam, the lava cooled. Conditions were such that the lava--that was incredibly uniform in its mineral composition--cooled at a very slow rate. As it cooled, it contracted and cracked, forming hexagonal columns. 80,000 years later, a glacier flowed through the same valley, overriding the formation and eventually revealing the sides and tops of the columns. Glacial polish can still be seen today at the top of the formation."
No comments:
Post a Comment