-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Related Web Page
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This earthcache is located within Lassen Volcanic National Park. There is a park entry fee of $30 per vehicle. The altitude at the Devastated Area is 6,453 feet. The half-mile interpretive trail is decomposed granite and wheelchair accessible.
From USGS Fact Sheet 173-98: On May 30, 1914, Lassen Peak awoke from a 27,000 year-long slumber. For a year the magma slowly rose in the vent and by mid-May 1915, more than 180 steam explosions had blasted out a 1,000 foot wide crater near the summit. On the evening of May 14, 1915, incandescent blocks of lava could be seen bouncing down the flanks of Lassen Peak. The next morning, a growing dome of dacite lava (lava containing 63 to 68% silica and therefore quite thick) had welled up into the volcano's crater and filled it. Late on the evening of May 19, a large steam explosion shattered the dacite dome, creating a new crater at the summit of Lassen Peak. No new magma was ejected in this explosion, but glowing blocks of hot lava from the dome fell on the summit and snow-covered upper flanks of Lassen Peak. These falling blocks launched a half-mile wide avalanche of snow and volcanic rock that roared 4 miles down the volcano's steep northeast flank and over a low ridge at Emigrant Pass into Hat Creek. As the hot lava blocks broke into smaller fragments, the snow melted, generating a mudflow of volcanic materials, called a lahar. The bulk of this lahar flowed 7 miles down Lost Creek. Huge volumes of water were released and lower Hat Creek was flooded during the early morning hours of May 20. Six summer ranch homes were destroyed but fortunately the people inside escaped. Late on the afternoon of May 22, after two quiet days, Lassen Peak exploded in a powerful eruption that blasted rock fragments and pumice high into the air, creating the larger and deeper of the two craters seen near the summit of the volcano today. A huge column of volcanic ash and gas rose more than 40,000 feet into the air and was visible from as far away as Eureka, 150 miles to the west. Pumice falling onto the northeastern slope of Lassen Peak generated a high-speed avalanche of hot ash, pumice, rock fragments, and gas, called a pyroclastic flow. This flow swept down the side of the volcano, devastating a 3 square mile area and mowing through stands of virgin forest that had survived the eruption three days earlier. The pyroclastic flow rapidly incorporated and melted snow in its path. The water from the melted snow transformed the flow into a highly fluid lahar that followed the path of the May 19 lahar and rushed nealry 10 miles down Lost Creek to Old Station. Hat Creek was flooded a second time. For several years after the May 22, 1915 eruption, spring snowmelt percolating down into Lassen Peak triggered steam explosions, indicating that rocks beneath the volcano's surface remained hot. By 1922, the volcano grew silent and has remained so. The Devastated Area remained largely devoid of vegetation for many years. Today it can be hard to tell that this once was a barren wasteland: natural reforestation is evident. References: USGS Fact Sheet 173-98. Michael Clynne, Robert Christiansen, Tracey J. Felger, Peter Stauffer, and James W. Hendley II Fire and Ice, The Cascade Volcanoes. Stephen L. Harris. 1980, Pacific Search Press Roadside Geology of Northern and Central California, 2nd Edition. David Alt, Donald W. Hyndman. 2016, Mountain Press Publishing Fire Mountains of the West, The Cascade and Mono Lake Volcanoes. Stephen L. Harris. 2005, Mountain Press Publishing Geology of the Lassen Country, The Geologic Story of Lassen Volcanic National Park & Vicinity. R. Forrest Hopson & Michael A. Clynne. 2019. Backcountry Press To claim this cache please respond to the following questions via e-mail. Please do not record your answers in your log or include any photos that would provide answers: 1. Provide the GC number and name of the cache. 2.Who was Elmer Sorahan and what is his significance in the eruptions of May 1915? 3. What kind of lava is the old giant? 4. What is a "survival forest" and how is it useful to park managers? At the base of what mountain is the "survival forest"? What kind of lava are the quenched blobs? Why did some rocks swept here by the pyroclastic flow (a "glowing avalanche" of rock &ash) fracture and others didn't?
Additional Hints
(No hints available.)