Lassen Peak 345248 221412761 2008-06-24T11:41:04Z Idioma-bot 2964546 robot Adding: [[lt:Laseno kalnas]] {{Infobox Mountain | Name=Lassen Peak | Photo=Lassen-Peak-Large.jpg | Caption=Lassen Peak and Devastated Area from Cinder Cone | Elevation={{convert|10457|ft|m|0}} | Location=[[California|California, USA]] | Range= [[Cascade Range]] | Prominence = {{convert|5229|ft|m|0}} | Coordinates = {{coord|40|29|17.42|N|121|30|18.03|W|type:mountain_region:US||display=inline}} | Topographic map = [[USGS]] Lassen Peak | Type=[[Lava dome]] | Volcanic_Arc/Belt=[[Cascade Volcanoes|Cascade Volcanic Arc]] | Age=&lt; 27,000 years | Last eruption=1917 | First ascent= | Easiest route=[[hiking|hike]] }} '''Lassen Peak'''<ref name="BGN">{{Gnis|262324|Lassen Peak}}</ref> (also known as '''Mount Lassen''') is the southernmost active [[volcano]] in the [[Cascade Range]]. It is part of the [[Cascade Volcanoes|Cascade Volcanic Arc]] which is an [[volcanic arc|arc]] that stretches from northern California to southwestern British Columbia. Located in the [[Shasta Cascade]] region of [[Northern California]], Lassen rises {{convert|2000|ft|m|-1}} above the surrounding terrain and has a volume of half a cubic mile, making it one of the largest [[lava dome]]s on Earth.<ref name="Eruptions of Lassen Peak">USGS: Eruptions of Lassen Peak, California, 1914 to 1917</ref> It was created on the destroyed northeastern flank of now gone [[Mount Tehama]], a [[stratovolcano]] that was at least a thousand feet (300&nbsp;m) higher than Lassen. Lassen Peak has the distinction of being the only volcano in the Cascades other than [[Mount St. Helens]] to erupt during the 20th century. On [[May 22]], [[1915]], an explosive eruption at Lassen Peak devastated nearby areas and rained [[volcanic ash]] as far away as 200 miles (320 km) to the east.<ref name="Eruptions of Lassen Peak"/> This explosion was the most powerful in a 1914–17 series of eruptions that were the last to occur in the Cascades before the [[1980 eruption of Mount St. Helens]] in [[Washington]]. [[Lassen Volcanic National Park]] was created in [[Shasta County, California]] to preserve the devastated area and nearby volcanic wonders. Unlike most lava domes, Lassen is topped by craters. In fact, a series of these craters exist around Lassen's summit, although two of these are now covered by solidified lava and sulfur deposits. Lassen is the largest of a group of more than 30 volcanic domes that have erupted over the past 300,000 years in the Lassen Volcanic Center. ==Climate== Lassen has the highest known [[snowfall]] amounts for California. With an average annual snowfall of 660&nbsp;[[inches]] (16.76&nbsp;[[Metre|m]]) , and some years receiving over 1,000&nbsp;inches (25.4&nbsp;m) of snow at its base of {{convert|8250|ft|m|0}} at [[Lake Helen (Lassen Peak)|Lake Helen]]. Mt. Lassen gets more precipitation (rain, [[hail]], melted snow) anywhere in the Cascades south of the [[Three Sisters (Oregon)|Three Sisters]] volcanoes.<ref>[http://www.skimountaineer.com/CascadeSki/CascadeSnow.html Ski Mountaineer]</ref> This heavy snowfall allows Lassen to retain 14 permanent patches of snow despite Lassen's modest elevation.<ref>[http://glaciers.pdx.edu/gdb/maps/california.php Glaciers of California], glaciers.pdx.edu (accessed [[4 January]] [[2008]])</ref> [[Lightning]] has been known to frequently strike the summit of the volcano during summer thunderstorms. == Geology == {{See|Lassen Volcanic National Park#Geology|Geology of the Lassen volcanic area}} [[Image:USA Lassen Peak CA.jpg|thumb|250px|Vulcan's Eye on Lassen Peak from Lake Helen]] Lassen is the southernmost in the chain of 18 large volcanic peaks that run from southwestern [[British Columbia]] to northern California. The peaks formed in the past 35 million years as the [[Juan De Fuca plate]] and the tiny [[Gorda plate]] to its south have been pulled under the overriding [[North American plate]]. As the [[oceanic crust]] in the Juan de Fuca plate melts under the pressure, it creates pools of [[lava]] that drive up the Cascade Range and power periodic eruptions in its volcanic peaks. Roughly 27,000 years ago,<ref name="Eruptions of Lassen Peak"/> Lassen started to form as a mound-shaped [[dacite]] lava dome pushed its way through Tehama's destroyed north-eastern flank. As the lava dome pushed its way up, it shattered overlaying rock, which formed a blanket of angular [[Scree|talus]] around the emerging steep-sided volcano (it looked much like the nearby 1,100-year-old [[Chaos Crags]]). Lassen rose and reached its present height in a relatively short time, probably in as little as a few years. From 25,000 to 18,000 years ago, during the last glacial period of the current [[ice age]], Lassen’s shape was significantly altered by [[glacial erosion]]. For example, the bowl-shaped depression on the volcano’s northeastern flank, called a cirque, was eroded by a glacier that extended out 7&nbsp;miles (11&nbsp;km) from the dome.<ref name="Eruptions of Lassen Peak"/> Lassen's most recent eruptive period started in 1914 and lasted for seven years (see below). The most powerful of these eruptions was a 1915 episode that sent ash and steam in a ten-kilometer-tall mushroom cloud, making it the largest recent eruption in the contiguous 48 U.S. states until the [[1980 eruption of Mount St. Helens]]. The region remains geologically active, with mud pots, active fumaroles, and boiling water features, several of which are getting hotter. The area around Mount Lassen and nearby [[Mount Shasta]] are considered the most likely volcanoes in the Cascade Range to shift from dormancy to active eruptions.<ref>EO Newsroom</ref> ==Human history== Before the arrival of white settlers, the areas surrounding Lassen Peak, especially in the east and south, were the traditional home of the (Northeastern) [[Maidu]]. Lassen Peak was named in honor of [[Denmark|Danish]] blacksmith [[Peter Lassen]], who guided immigrants past the peak to [[Sacramento Valley]] in the 1830s. Lassen's trail, however, never found general long-term use because it was considered unsafe. [[Nobles Emigrant Trail]], named after [[William Nobles]], which linked Applegate Trail in Nevada to Northern Sacramento Valley, replaced it. In 1864 [[Helen Tanner Brodt]] became the first woman to reach the summit of Lassen Peak. A [[tarn (lake)|tarn]] (lake in a [[cirque (landform)|cirque]] basin) on Lassen was named Lake Helen in her honor. Starting in 1914 and ending in 1921 Lassen came alive with a series of [[phreatic eruption]]s (steam explosions), dacite lava flows, and [[lahar]]s (volcanic mud flows). There were 200 to 400 [[volcanic eruption]]s during this period of activity. First-hand accounts of the time record at least one fatality, in 1915. ==Early 20th century eruptions== [[Image:May 1915 Lassen eruption column.jpg|thumb|<small>The "Great Explosion" eruption column of May 22, 1915 was seen as far as {{Convert|150|mi|km|0|abbr=on}} away (Photograph by R.E. Stinson)</small>]] [[Image:Lassen Peak Before 1914.jpg|thumb|<small>Mount Lassen Before 1914</small>]] [[Image:Lassen Peak in June 1915.jpg|thumb|<small>Lassen Peak in June 1915 with Loomis Hot Rock, one of the many large boulders set loose in the eruption that were too hot to touch for days after, in the foreground (photgraph by B.F. Loomis; [[media:Loomis Hot Rock-750px.JPG|modern photo]])</small>]] ===Initial rumblings (May 1914 to May 1915)=== On [[May 30]], [[1914]], Lassen became active again after 27,000 years dormancy when it was shaken by a steam explosion. Such steam blasts occur when molten rock ([[magma]]) rises toward the surface of a volcano and heats shallow [[ground water]]. The hot water rises under pressure through cracks and, on nearing the surface, vaporizes and vents explosively. By mid-May 1915, more than 180 steam explosions had blasted out a 1,000&nbsp;ft (300&nbsp;m) wide crater near the summit of Lassen Peak.<ref name="Eruptions of Lassen Peak"/> Then the character of the eruption changed dramatically. On the evening of [[May 14]], [[1915]], incandescent blocks of [[lava]] could be seen bouncing down the flanks of Lassen from as far away as the town of [[Manton, California]] 20&nbsp;miles (30&nbsp;km) to the west.<ref name="Eruptions of Lassen Peak"/> By the next morning, a growing dome of [[dacite]] lava (lava containing 63 to 68% [[silica]]) had filled the volcano’s crater. ===Events of May 19–20, 1915=== Late on the evening of [[May 19]], a large steam explosion fragmented 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 Mount Lassen. These falling blocks launched a half mile (800 m) wide avalanche of snow and volcanic rock that roared {{Convert|4|mi|km|0|abbr=on}} down the volcano’s steep northeast flank and over a low ridge at Emigrant Pass into Hat Creek.<ref name="Eruptions of Lassen Peak"/> 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 was deflected northwestward at Emigrant Pass and flowed 7&nbsp;miles (11&nbsp;km) down Lost Creek.<ref name="Eruptions of Lassen Peak"/> Even after coming to rest, both the avalanche and lahar released huge volumes of water, flooding the lower [[Hat Creek Valley]] during the early morning hours of [[May 20]]. The lahar and flood destroyed six mostly not-yet-occupied summer ranch houses. Fortunately, the few people in these houses escaped with only minor injuries. Also during the night of May 19–20, dacite lava somewhat more fluid than that erupted on the night of May 14–15 welled up into and filled the new crater at Lassen’s summit, spilled over low spots on its rim, and flowed 1,000&nbsp;feet (300&nbsp;m) down the steep west and northeast flanks of the volcano.<ref name="Eruptions of Lassen Peak"/> ===Climactic eruption of May 22, 1915=== Then at 4:30 p.m. on [[May 22]], after two quiet days, Lassen exploded in a powerful eruption (referred to as "the Great Explosion") that blasted volcanic ash, rock fragments and pumice high into the air. This created 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 30,000 feet (9,000 m) into the air and was visible from as far away as [[Eureka, California]] {{convert|150|mi|km|0}} to the west.<ref name="Eruptions of Lassen Peak"/> 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]], that swept down the side of the volcano, devastating a {{convert|3|sqmi|km2|0}} area.<ref name="Eruptions of Lassen Peak"/> 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 19–20 lahar and rushed nearly {{convert|10|mi|km|0}} down Lost Creek to Old Station. This new lahar released a large volume of water that flooded lower Hat Creek Valley a second time. The powerful climactic eruption of [[May 22]] also swept away the northeast lobe of the lava flow extruded two days earlier. The eruption produced smaller mudflows on all flanks of Lassen Peak, deposited a layer of volcanic ash and pumice traceable for 25&nbsp;miles (40 km) to the northeast, and rained fine ash at least as far away as [[Winnemucca, Nevada]], 200 miles (320 km) to the east.<ref name="Eruptions of Lassen Peak"/> Together these events created the Devastated Area which is still sparsely populated by trees due to the low [[nutrient]] and high porosity of the [[soil]] there. ===Later volcanic activity=== For several years after the [[May 22]], 1915, eruption, spring snowmelt percolating down into Mount Lassen triggered steam explosions, an indication that rocks beneath the volcano’s surface remained hot. Particularly vigorous steam explosions in May 1917 blasted out the second of the two craters now seen near the northwest corner of the volcano’s summit (two older craters are buried).<ref name="Eruptions of Lassen Peak"/> Steam vents could be found in the area of these craters into the 1950s but gradually waned and are difficult to locate today. Since then, the [[USGS]] in cooperation with the [[United States Park Service]] have been monitoring Lassen and other volcanic and [[geothermal areas in Lassen Volcanic National Park|geothermal areas in the park]]. [[Image:Deposits from May 1915 eruption of Lassen Peak.jpg|center|600px|thumb|Deposits from May 1915 eruption of Lassen Peak (USGS map)]] {{wide image|USA Lassen NP Kings Creek CA edit3.jpg|1000px|<center>''Kings Creek with Lassen Peak on the horizon''</center>}} ==See also== *[[Cascade Range#High Cascades|High Cascades]] *[[Geology of the Pacific Northwest]] *[[Lassen Volcanic National Park]] *[[Volcanic Legacy Scenic Byway]] *[[List of highest points in California by county]] ==References== ===Major works cited=== *''Geology of National Parks: Fifth Edition'', Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7 *[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17170 EO Newsroom (NASA)], New Images of Lassen Volcanic National Park (adapted public domain text; accessed [[18 September]] [[2006]]) *[http://pubs.usgs.gov/fs/1998/fs173-98/ Eruptions of Lassen Peak, California, 1914 to 1917], U.S. Geological Survey Fact Sheet 173-98 (adapted public domain text; accessed [[18 September]] [[2006]]) ===Notes=== {{reflist}} ==External links== *[http://www.nps.gov/lavo/ The Official Lassen Volcanic National Park Web Site] *[http://pubs.usgs.gov/fs/1998/fs173-98/ USGS: Eruptions of Lassen Peak, California, 1914 to 1917] *{{VNUM|1=1203-08-}} {{Geolinks-US-mountain|40.48817|-121.50501}} {{Cascade volcanoes}} [[Category:Cascade Range]] [[Category:Mountains of California]] [[Category:United States National Park high points]] [[Category:Shasta County, California]] [[Category:Volcanoes of California]] [[Category:Lassen Volcanic National Park]] [[Category:Subduction volcanoes]] [[Category:Lava domes]] [[Category:Cascade Volcanoes]] [[Category:VEI-3 volcanoes]] [[de:Lassen Peak]] [[et:Lassen Peak]] [[fr:Lassen Peak]] [[hi:लैसेन पीक]] [[it:Lassen Peak]] [[lt:Laseno kalnas]] [[nl:Lassen Peak]] [[ja:ラッセン山]] [[sk:Lassen Peak]] [[fi:Lassen Peak]] [[vi:Đỉnh Lassen]]