Mount Baker—Living with an Active Volcano
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USGS U.S. GEOLOGICAL SURVEY—REDUCING THE RISK FROM VOLCANO HAZARDS Mount Baker—Living with an Active Volcano VOLCANO HAZARDS AT MOUNT BAKER LAVA FLOWS Lava is molten rock (magma) that pours or oozes onto the Earth's surface. Numerous eruptions of lava interbedded with rock rubble constructed Mount Baker. PYROCLASTIC FLOWS Pyroclastic flows are hot avalanches of lava fragments and volcanic gas formed by the Mount Baker (10,781 feet) viewed from east side with steam plume rising from Sherman Crater (left side of summit, inset shows crater interior). Scar of the 1891 flank collapse is visible in lower left of photo. Photos by collapse of Kevin Scott and (inset) Robert Symonds, USGS. lava flows or What Are the Hazards? eruption ount Baker dominates the clouds. M skyline from Bellingham, The next eruption of Mount Baker may Washington, and Vancouver, British produce lava flows, pyroclastic flows, volcanic ash (tephra), and lahars. Lahars are Columbia. On cold, clear winter TEPHRA by far the greatest concern at Mount Baker Explosive eruptions days, dramatic increases in the because of its history of frequent lahars, the blast fragments of steam plume rising continuously ability of lahars to flow for tens of miles, and rock high into the air. from Sherman Crater can alarm the potential for hazardous future impacts of Large fragments local residents. This apparent lahars on two reservoirs on the east side of the fall to the ground increase in plume vigor occurs volcano. Tephra hazards at Mount Baker are close to the volcano. because of condensation of steam less important than at neighboring Glacier Peak in cold, calm air. In 1975, however, Small fragments volcano to the south. (called ash) increased steaming and melting of Lahars can originate in two ways: from the largest snow and ice around Sherman 1) During eruptions, pyroclastic flows can eruptions can Crater did signify a change in heat melt snow and ice to create torrents of ash, travel hundreds output from the volcano's interior. rock, and water that move downvalley as sandy of miles. Although the increased heat flow (noncohesive) lahars. 2) Because the volcano is locally weakened gradually subsided, it could have LAHARS signaled the start of eruptive and altered to clay by percolating, acidic, hot water and steam (like that venting from activity, and precautions were Lahars are fast-moving slurries of wisely undertaken. Sherman Crater), future volcanic landslides rock, mud, and water that look and So that the public can be warned known as flank collapses can mobilize to form behave like flowing wet concrete. of, and be prepared for, future muddy (cohesive) lahars. eruptions and other hazardous Lahars of collapse origin occur during Landslides can eruptions. They also occur during non-eruptive transform into lahars. events at Mount Baker, U.S. Geo- Pyroclastic flows can logical Survey (USGS) scientists periods triggered by regional earthquakes, gravity, or increases in hydrovolcanic activity generate lahars are studying the volcano's past not associated with magma intrusion. by melting behavior and monitoring its current When ground water comes in contact with snow and ice. activity. either magma or hot rock, hydrovolcanic U.S. Department of the Interior USGS Fact Sheet-059-00 U.S. Geological Survey May 2000 Deposit of the largest lahar from Mount Baker, exposed near the confluence of the Middle and North Forks of the Nooksack River, about 20 miles from its source at the Roman Wall. Note the protruding logs and branches from living trees that were knocked down and carried by the lahar. Ice axe, 3 ft, shows scale. Lahars are the greatest hazard at Mount Baker. Inset shows the flow front of a slurry of rock and water, typical of lahars. The flow is about 10 feet deep, moving right to left at 20 miles per hour. Photos by Kevin Scott, USGS. explosions of steam and rock can occur. Such 400,000 and 300,000 years ago and formerly events, in addition to possibly triggering bigger than today's Mount Baker. collapse, can themselves be hazardous. Although numerous in Oregon and southern Volcanic ash (tephra) layers on Mount Baker's south Washington, cinder cones formed of the rock flank. Lower white band is from an eruption of Crater Mount Baker— Early History type called basalt are rare around Mount Baker. Lake, Oregon (7,700 years ago); upper yellow band is USGS research in the last decade shows A cinder cone that formed 9,800 years ago in from a hydrovolcanic eruption of Mount Baker (6,600 Mount Baker to be the youngest of several years ago). Above the yellow band is a black ash from Schriebers Meadow produced a widespread a magmatic eruption of Mount Baker (also about volcanic centers in the area and one of the tephra layer, and lava flows that reached the 6,600 years ago). Tephra hazards at Mount Baker are youngest volcanoes in the Cascade Range. Vol- Baker River. less significant than at neighboring Glacier Peak canic activity in the Mount Baker area began volcano to the south. Photo by Kevin Scott, USGS. more than one million years ago, but many of Today's Mount Baker the earliest lava and tephra deposits have been Modern Mount Baker formed during and south of the summit. Both these area are sites removed by glacial erosion. The pale-colored since the last ice age, which ended about of pervasive bedrock alteration, converting rocks northeast of the modern volcano mark 15,000 years ago. Lava flows from the summit lavas to weak, white-to-yellow material rich in the site of ancient Kulshan Caldera that vent erupted between 30,000 and 10,000 years clays, silica, and sulfur-bearing minerals. At collapsed after an enormous ash eruption one ago and, during the final stages of edifice Sherman Crater, collapses of this weakened million years ago. Subsequently, eruptions in construction, blocky pyroclastic flows poured rock created lahars in 1843 and as recently as the Mount Baker area have produced cones and down most of the volcano's drainages. An the 1970's. lava flows of andesite, the rock that makes up eruption 6,600 years ago produced a blanket of much of other Cascade Range volcanoes like ash that extended more than 20 miles to the Past Events — Future Hazards Mounts Rainier, Adams, and Hood. From about northeast. This eruption probably occurred Like most volcanoes, Mount Baker's history 900,000 years ago to the present, numerous from the presently ice-filled summit crater. records great variations in behavior. Scientists andesitic volcanic centers in the area have Subsequently, sulfurous gases have found two believe the following case histories are good come and gone, eroded by glaciers. The largest pathways to the surface—Dorr Fumaroles, examples of the range in size and types of is the Black Buttes edifice, active between northeast of the summit, and Sherman Crater, hazardous activity that have occurred in the Eruptions and flank collapses at Mount Baker Sequence of events about 6,600 years ago Historical events during the past 12,000 years Large Hydrovolcanic Ash Hydrovolcanic collapse, explosion, eruption explosion, Increased large collapse, collapse, Collapse, steam and lahar large lahar lahars lahar heat Multiple lava flows, pyroclastic flows, AD 1843 1891 1975 ash eruptions, noncohesive lahars Cinder Collapse, Collapse, cone lahar lahar 12 10 8 6 4 2 0 THOUSANDS OF YEARS AGO Sumas Lynden Maple Falls sa 542 rth Nook ck River No Fork Everson Glacier Deming M Kulshan i d d Caldera l e Mount F o rk N Roman Wall Baker Dorr Fumaroles ook 9 sa Sherman Crater ck Bellingham R. Black Buttes Bellingham Bay Lake Whatcom Baker Schriebers Meadow Lake 5 Cinder Cone WHATCOM COUNTY SKAGIT COUNTY r e v i Lake R r Shannon e k a Concrete B River Skagit 20 Sedro Woolley Burlington EXPLANATION Inundation Zone I - Pathways for eruption-related lahars due to large flank collapses or pyroclastic flows, or floods in the Skagit River valley caused by displacement of water in reservoirs by lahars. Mount Vernon Inundation Zone II - Pathways of lahars resulting from more frequent, small-to-moderate flank collapses from the area of Sherman Crater. 0 5 10 Miles Proximal pyroclastic flowage hazard zone - Area that could be affected by pyroclastic flows and lava flows. Map showing hazard zones for lahars, pyroclastic flows and lava flows (for more detail see Plate 1 in US Geological Survey Open-File Report 95-498). past and could occur again. Small events are the site of present day Sherman Crater, reported that many salmon were killed. A short more common than large ones, and during a triggering a second collapse of the flank just time later, two collapses of the east side of future hazardous event only parts of the hazard east of the Roman Wall. That collapse also Sherman Crater produced two lahars, the first zones shown on the map may be affected. became a lahar that mainly followed the course and larger of which flowed into the natural of the first one for at least 20 miles, but also Baker Lake, raising its level at least 10 feet. Flank Collapses, Lahars, and Tephra spilled into tributaries of the Baker River. The location of this 19th-century lake is now Eruptions, about 6,600 Years Ago Finally, an eruption cloud deposited several covered by waters of the modern dam- A series of discrete events culminated with inches of ash as far as 20 miles downwind to impounded Baker Lake. Similar but lower level the largest tephra-producing eruption in post- the northeast. glacial time at Mount Baker. First, the largest hydrovolcanic activity at Sherman Crater collapse in the history of the volcano occurred Sherman Crater Forms in 1843 continued intermittently for several decades from the Roman Wall (see map) and trans- The present shape of Sherman Crater afterwards.