Thursday, September 19, 2013

Devastated Area Interpretive Trail in Lassen Volcanic

Old Giants: red dacit formed at Lassen_Peak 27,000 years ago

The Devastated Area Interpretive Trail in Lassen Volcanic National Park, California, is a short, wheelchair-accessible loop trail with interpretive and audio exhibits that feature aftermath evidence of Lassen Peak's catastrophic eruptions in May of 1915. Businessman, photographer, and author, Benjamin F. Loomis—Lassen Park's Loomis Museum is named in memory of his daughter Mae—came to inspect this area after one eruption, when the next one was following. An on-site panel describes that event:
On May 22, 1915, seven men, including photographer B. F. Loomis, passed near here while inspecting the damage that followed Lassen Peak's May 19 eruption. They were astounded by what they saw, but could not suspect that the horrific scene would be repeated just hours later. Had they dallied they might not have survived, for Lassen Peak blew again at 4:45 p.m. that afternoon.

Black dacite
Large lava rocks blasted from Lassen crater and were carried for many miles by avalanches to finally rest as monuments throughout what became to be the Devastated Area. Rocks of the May 19 and May 22 eruptions are aligned at the interpretive exhibit with the title New Rocks, Old Rocksblack dacite, banded pumice and light dacite pumice. An older rock that formed during an eruption about 27,000 years ago is the red dacite. Another “old-rock” red dacite is the giant boulder at the Old Giants exhibit. It is shown in the top picture. The panel says that it formed 27,000 years ago, when Lassen Peak first erupted, and was torn from the volcano via avalanche caused by the May 19 eruption.

Other exhibits along the loop trail showcase the legacy of B. F. Loomis, who photo-chronicled Lassen Peak's eruptions and glowing lava rocks. Further exhibits illustrate the mixing and solidification of basalt-injected dacite lava and the fracturing of cooling rocks into jigsaw-puzzle-like pieces.

Light dacite_pumice
If you are interest in rocks that have been shaped and altered by geothermal activity, you can find examples inside the Loomis Museum. A wall exhibit displays various specimen including Bumpass Hell sulfurous andesite, Sulfur Works quartz-pyrite pseudomorph, weathered Chaos Crags dacite and alunite-dusted clay.


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