Effects of volcanism on the glaciers of Mount St. Helens

Abstract

METRIC CONVERSION FACTORS Multiply foot (ft) cubic yard (yd 3) mile (mi) square mile (mi 2) cubic foot per second (ft 3 /sec) cubic mile (mi 3) By 0.3048 0.7646 1.609 2.590 .02832 FOREWORD On May 18, 1980, after more than a month of earthquakes and eruptions, Mount St. Helens, in southwestern Washington, exploded in a volcanic eruption more violent than any in the conterminous United States during the 20th century. A lateral blast of hot gas and rock particles devastated an area of about 150 square miles on the northern side of the mountain knocking down trees to a distance of 15 miles. Several minutes later, a giant ash cloud rose to about 60,000 feet. Winds then carried the ash cloud across the United States, with heavy fallout and deposition in eastern Washington and parts of Idaho and Montana. Earlier, smaller eruptions deposited ash in western Washington and parts of Oregon and Canada. The hydrologic effects of the May 18 eruption have been both widespread and intense. During the eruption, a massive debris avalanche moved down the north flank of the volcano depositing about 3 billion cubic yards of rock, ice, and other materials in the upper 17 miles of the North Fork Toutle River valley. The debris deposits are about 600 feet thick in the upper reaches of the valley. Following the avalanche, runoff from the melted glaciers and snow, and possible outflow from Spirit Lake, caused an extraordinary mudflow in the North Fork Toutle River. The mudflow shattered and uprooted thousands of trees, destroyed most of the local bridges, and deposited an estimated 25,000 acre-feet of sediment in the Cowlitz River channel. A considerable amount of additional sediment was conveyed through the lower Cowlitz into the Columbia River where it deposited and formed a shoal that blocked the shipping channel. Mudflows also occurred in the South Fork Toutle River and in tributaries on the east flank of Mount St. Helens which enter Swift Reservoir. As part of a concerted Geological Survey effort to study the volcanic event and to identify potential hazards, Survey hydrologists have mounted an intensive program to document the hydrologic effects of the eruptions. The major initial hydrologic findings are reported in this circular series. Quick, useful assessment was made possible only because the Survey has long conducted extensive waterresources investigations in the affected areas of Washington, Oregon, and Idaho. Hence, there was a well-defined basis for identification and documentation of the types and magnitudes of hydrologic changes. The Geological Survey Circular 850, "Hydrologic Effects of the Eruptions of Mount St. Helens, Washington, 1980," consists of individually published short chapters that emphasize data collection activities, field observations, and initial comparisons of pre-and post-eruption conditions. The series will cover hydrologic events occurring on May 18 in the Toutle and Cowlitz River; physical alteration of the Toutle River system; the chemical and physical quality of precipitation, streams, and lakes affe...

Field-trip guide to Mount St. Helens, Washington - An overview of the eruptive history and petrology, tephra deposits, 1980 pyroclastic density current deposits, and the crater

“…This second, laterally directed blast flowed outward and merged with the first, overtaking the debris avalanche and engulfing Mount St. Helens (Hoblitt, 2000). Snow and ice was stripped from the volcano, eroding about 6 m off Shoestring Glacier (Brugman and Post, 1981). Within 6 minutes of the first earthquake, the currents traveled as far as 28 km north and devastated 600 square kilometers (km 2 ) of rugged, densely forested terrain.…”

Inventory and Initiation Zone Characterization of Debris Flows on Mount St. Helens, Washington Initiated during a Major Storm Event in November, 2006

“…Glacier #2 is the Snowfield Glacier, which today exists only as a permanent snowfield. Redrawn from Brugman and Post (1981) and extent. In existence as of 2009 are the glaciers: Nelson, Ape, Shoestring, June (#1), and Swift.…”

On the geochronological method versus flow simulation software application for lahar risk mapping: a case study of popocatépetl volcano, mexico

“…There are no reports of lahars generated by 100% of the glacier melting in the Popocatépetl volcano. However, the case of Mt St Helens (USA) in 1980 can once again be used to illustrate how an eruption can destroy part of the volcano and make a glacier disappear, as happened in the case of the Loowit and Leschi glaciers (Brugman and Post 1981). As in the previous scenario, the probability for a lahar generated by a sudden melting of 100% of the glacier in Popocatépetl volcano is once every 4000 years.…”

“…To calculate the probability of this happening at Popocatépetl, we consider a similar case which occurred on 18 May 1980 at Mt St Helens (USA) where several lahars occurred when the summit of the volcano blew out generating the failure of the flank of the edifice resulting in a volcanic avalanche. Some of the glaciers at Mt St Helens were dramatically affected by this eruption such as the Shoestring, Forsyth, Wishbone, Ape and Nelson glaciers (Brugman and Post 1981). Popocatépetl volcano has reported several volcanic avalanches facing to the south of the volcanic edifice and related to Bezymianny eruptions.…”