Monday, January 17, 2011

What a Geologist Sees - Part 29 [Original Post Date 10/02/09]

Shatter Ring on PKK Lava Tube (March 20-22, 2006) from this USGS site:

This video, shot by Tim Orr of the USGS, is of interest as I studied these Shatter Rings in the Aden Basalts of southern New Mexico. Not aware of the existence of other examples (20 years ago), we called them "Explosion-collapse" craters and I described 5 of them in my Master's Thesis.

Using the description from the USGS website, here is a description of the Shatter Rings:

"Shatter rings are circular to elliptical volcanic features, typically tens of meters (yards) in diameter, which form over active lava tubes. They are typified by an upraised rim of blocky rubble and a central depression."..."They form when lava pressure in the tube repeatedly exceeds the strength of the overlying rock. Repeated flexing of the lava-tube roof piles up rubble around the edges of the mobile area."

In the case of the shatter rings I studied, lava was extruded up through the shattered rocks and filled-in the bottom of the crater, creating a lava lake, which later collapsed after the lava below withdrew.

When I scan some more of my old slides and prints from my field area, I will write more about these features.

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