Friday, August 14, 2015

Lava Tubes: Day 260


Near the summit of Bogoslof Hill, one of St. Paul's extinct volcanic peaks, is an extensive lava tube reaching a few hundred yards into the heart of the island. During an eruption, lava tends to spill out of the source point in discrete channels. Like an artery of super-heated rock, the lava begins to solidify and forms an exterior crust, creating tubular walls of rock that insulate the hot lava flowing within. Eventually the pressures forcing magma up from chambers deep inside the volcano subside, closing the valve on the eruption. Deprived of lava, the volcanic arteries drain and cool, leaving behind vast empty tubes of black volcanic rock. The round dome-like chamber in this photo was accessed through a narrow slit off the main lava tube, which I believe is actually a type of "inflationary cave", where a bubble of pressurized lava pushed back against the surrounding rock and later drained into the main channel.

Canon EOS 60D, Canon EF 17-40mm f/4L USM, ISO-200 f/4 @ 30 seconds.

1 comment:

  1. I'm going to St. Paul Island in June. Is this cave easy to find once at the summit of Bogoslof Hill?

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