The 1980 Mount St. Helens Eruption: Prelude to Geological Advancement

By: Antonio Kornegay

In many ways, May 18, 1980 was a monumental day. Firstly, this was the day which Washington’s Mount St. Helens erupted, wreaking havoc on everything in its midst. However, this fateful day also marked the genesis of a series of breakthroughs which shook the scientific world. While the Washington-based stratovolcano gained notoriety for its horrific eruption, which sent its summit flying in a high-velocity avalanche, US government agencies and volcanologists were hard at work, endeavoring to acquire understanding about this natural disaster. In the midst of such endeavors, volcanologists discovered something that redefined volcanic knowledge at the time—the collapse of Mount St. Helens’ summit was caused by edifice failure, or partial volcanic collapse. In addition to this landmark breakthrough, volcanologists also made progress on volcanic monitoring techniques, based on research performed on Mount St Helens after the 1980 eruption. Because of the magnitude of the edifice failure discovery and the progress made in volcanic monitoring techniques, the 1980 Mount St. Helens had a colossal impact of the geological community.

Mount St. Helens eruption, May 18, 1980 at 8:32am. Taken by Austin Post, United States Geological Survey.

Since Mount St. Helens was a stratovolcano, some background information about stratovolcanoes would prove useful in understanding this mammoth structure. Stratovolcanoes, alternately called composite volcanoes, are usually symmetrical, cone-like structures whose steepness varies in such a manner that produces a upward concave formation, curving inward from the bottom to the top of the mountain (How Volcanoes Work: Stratovolcanoes 2006).Internally, stratovolcanoes are normally composed of alternating sections of lava flows, volcanic mudflows, ash, and other types of volcanic matter (How Volcanoes Work… 2006). Typically, stratovolcanoes feature ventilated crater walls where lava can flow through, contributing to as much as a 2400 ft increase in height, as the lava cools (McLean and Lockridge 4). Such height climb can also be attributed to a conduit system which allows magma to rise from underground reservoirs to the Earth’s surface (McLean and Lockridge 2000). Often found at convergent, or collisional,  crustal plate margins, stratovolcanoes are often characterized by violent Plinian eruptions, violent eruptions which send a large plumes of toxic gas and volcanic ash into the atmosphere at supersonic speeds (How Volcanoes Work… 2006).

Precursory Eruption of Mount St Helens, April 7, 1980. Taken by Peter W. Lipman, United States Geological Survey

Since the May 18, 1980 Mount St. Helens eruption occurred, scientists conducted studies on the precursory events leading up to the eruption, in effect making huge strides in volcanic monitoring, especially as it relates to predicting eruptions.  While studying the magmatic precursors of the 1980 Mount St Helens catastrophe, geologists K.V. Cashman and R.P Hoblitt observed that there was juvenile, or new, magma in the ash from previous small eruptions, ranging from 2-25 percent concentration (Cashman and Hoblitt 2004). Since the presence of juvenile magma in precursory ash is indicative of magma intrusion, Cashman and Hoblitt concluded that the explosive power of volcanoes can be determined from the monitoring of juvenile magma in precursory eruptions (Cashman and Hoblitt 2004). These findings can enable geologists to predict when future volcanoes could erupt and estimate its explosive power, thus making an extreme contribution to the geological community.

In addition to enhancing volcanic monitoring techniques, the 1980 Mount St. Helens eruption also changed the tide of volcanic thought through the edifice failure theory. In “Blown Away” Lee Siebert discusses how just one natural disaster could cause such a monumental shift in volcanic theory. During the eruption, Mount St Helens’ summit detached from the mountain to form an avalanche, leaving a horseshoe-shaped crater, or caldera in the mountain. According to Siebert, studies conducted by the U.S. Geological Survey found that the volume of the avalanche debris matched closely to that of St Helens’ summit (Siebert 2005). These findings allowed researchers to conclude that the caldera was caused by the avalanche, refuting the popular belief that the volcanic explosion “blew the top off the volcano” (Siebert 2005).

Mount St. Helens' Caldera, May 19, 1982. Taken by Lyn Topinka, United States Geological Survey.

Along with disproving popular belief, these findings prompted scientists to reevaluate other faraway volcanic deposits from structures including Java’s “Ten Thousand Hills of Tasikmalaya,” which was mistakenly concluded to be handiwork of local farmers (Siebert 2005). From these reexaminations, scientists discovered that these volcanic deposits, and the calderas they leave behind, are the result of edifice failure (Siebert 2005). Typically, edifice failure occurs under any of three conditions. First, rock slippage can occur when magma is high in the volcano’s edifice, causing a lateral blast, as was the case during the 1980 Mount St Helens’ eruption (Siebert 2005). Secondly, a volcano’s edifice could still collapse without a lateral blast and expel magma (Siebert 2005). Lastly, a volcano’s edifice could collapse, expelling only ash and steam (Siebert 2005).  The edifice failure discovery destroyed the notion that structural volcanic collapse was a rare occurrence, thus carrying great geological significance by changing the course of volcanic theory.

Thanks to a Washington-based stratovolcano, science will never be the same. The 1980 Mount St Helens eruption prompted such studies which not only contributed to volcanic monitoring techniques, but also altered the course of volcanic understanding with the edifice failure discovery. The edifice failure phenomenon, once considered a rarity, became one of the primary causes for caldera formation during volcanic eruptions. Consequently, over 400 volcanoes have currently been indicated to have experienced edifice failure (Siebert 2005). Therefore, because of the weight the advances made in volcanic monitoring and the edifice failure discovery, the May 18, 1980 Mount St Helens eruption was geologically significant.

Works Cited

Cashman K.V, Hoblitt R.P . 2004. Magmatic precursors to the 18 May 1980 eruption of Mount St. Helens, USA. Geology [Internet]. [cited 2010 Nov 16];  32(2): 141-144. Available from: http://geology.geoscienceworld.org/cgi/content/full/32/2/141

McLean S, Lockridge P. 2000. A Teacher’s Guide to Stratovolcanoes of the World [Internet]. National Geophysical Data Center . [cited 2010 Nov 16]; 64 p. Available from: http://www.ngdc.noaa.gov/hazard/stratoguide/stratoguide.pdf

Siebert L. 2005. Blown Away. Nat.  Hist. [Internet]. [cited 2010 Nov 16];  114(8): 50-55. Available from Academic  Search Premier: http://ehis.ebscohost.com/ehost/detail?vid=12&hid=4&sid=db9d0e31-a571-4399-8b73-20e6e11016bc%40sessionmgr11&bdata=JnNpdGU9ZWhvc3QtbGl2ZSZzY29wZT1zaXRl#db=aph&AN=18474073

How Volcanoes Work-Stratovolcanoes (1980) [Internet ]. San Diego (CA): San Diego State University. [updated 31 Mar 2006; cited 2010 Nov 16]. Available from: http://www.geology.sdsu.edu/how_volcanoes_work/stratovolc_page.html