The Explosive History of Volcanoes in the U.S.

Mount St. Helens prior to eruption. Photo credit to USGS

Mount St. Helens prior to eruption. Photo credit to USGS

Nicholas Silva, Layout Editor

Recently the Kilauea volcano in Hawaii has been spewing out molten lava and wreaking havoc on the Big Island. However, there are over 160 possibly active volcanoes across the United States alone, so there is certainly a vast history to pull from.

Volcanoes are rated in intensity on a scale known as the Volcanic Explosivity Index (VEI) which was developed in 1982 by Chris Newhall and Stephen Self of the United States Geological Survey (USGS) and the University of Hawaii respectively. The scale is similar to the Richter magnitude scale for earthquakes, and is measured from 1-8, with one being the least severe.

Old Faithful Geyser in Yellowstone National Park. Photo Credit to NPS / Jacob W. Frank

There have been very few VEI-8 eruptions in history, and none in recent history. One of the worst eruptions in ‘recent’ history is believed to have been in Yellowstone. Yellowstone is, in fact, a super volcano. The site is believed to have erupted about 640,000 years ago. The USGS figures that the eruption produced enough lava and ash to easily fill the entirety of the Grand Canyon. Researchers now believe that there is eleven times that amount of magma. The super volcano is expected to erupt every 700,000 years or so, according to a recent study.

Another active American volcano is Cleveland Volcano located on the Aleutian Islands off of Alaska. The volcano is known for short bursts of ash, and very little lava, in an all bark no bite sort of way. The volcano did however produce a ten-kilometer high column of ash in May 1994. It is also responsible for the death of a soldier that was stationed on the island in June 1944. The volcano is presently one of the only volcanos in the U.S. that is at a yellow alert, and sometimes even an orange alert, meaning that it shows significant activity indicative of eruption, or is likely to erupt.

In July 1990, a category 8 earthquake in the Philippines rocked Mount Pinatubo, located in the center of the region. After several small steam eruptions in the April of 1991, the volcano fully

erupted on June 15, 1991. The eruption was a VEI-6, and produced a plume of ash reminiscent of the mushroom cloud of a nuclear bomb. Volcanologists used software known as RSAM (real-time seismic amplitude measurement) to predict the area that might be affected by the eruption. As it turns out, the predictions were very close. Specialists decided that the safest position in case of an evacuation would be Naval Station Subic Bay and Naval Air Station Cubi Point, both about 25 miles away from Pinatubo.

Mount Pinatubo erupting. Photo credit to USGS.

By June 10th, the volcano was showing more signs of activity, and all civilians and nonessential military personnel were sent to the evacuation areas. Volcanologists and other essential personnel pulled back five miles. On June 12th, a plume of ash was sent about twelve miles into the air, and the following day yet more activity was recorded. On June 15th the volcano finally erupted, and according to the USGS sent “Huge avalanches of searing hot ash, gas and pumice fragments, called pyroclastic flows, roared down the flanks of Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as 660 feet thick.” The eruption was so significant, and so much magma and ash expelled, that the mountain caved in, forming a nearly two mile crater.

The area was buried under ash. Many buildings were destroyed by sheets of lava, and bridges were demolished as far as eighteen miles away due to river-bound debris. More than 840 people were killed, many because of collapsed roofs caused by buildups of wet, heavy ash.  There was also an extreme period of rain-induced floods which picked up volcanic material and triggered subsequent landslides and mudflows for years to come, making recovery a difficult task. In all, the eruption lowered global temperature by one degree Fahrenheit.

Finally, the volcano that most people think about is Mount St. Helens. Starting March 16th, 1980, small earthquakes were observed in the area near the dormant volcano. Volcanologists were intrigued, and began to observe the location. Hundreds of small earthquakes were recorded.

March 17th, 1980, saw a massive steam explosion which tore a 1,300 foot wide hole out of the mountain’s summit. After another 10,000 earthquakes in a one month period, the side of Mount St. Helens had bulged out 450 by May 17th. This dramatic transformation drew much concern from researchers.

Mount St. Helens soon after the May 18, 1980 eruption. Photo credit to USGS.

The following day, a 5.1 earthquake was recorded near the mountain, and within seconds the bulge fell away from the side of the volcano in what is regarded as the most massive landslide in recorded history. The landslide destabilized the magma stored below it, and the volcano erupted viciously, flinging lava, ash, and rocks at speeds exceeding 300 miles per hour.

The cloud of dust and debris emitted by the volcano traveled as far away as seventeen miles in a very short amount of time. The disturbance sent lava and ash up to 15 miles into the air within just 15 minutes. This eruption was swiftly followed by an eruption from the volcano’s crater an hour later. By the end of the 18th, an estimated 520 million tons of ash was distributed across the United States by the wind. In some cases, this ash induced utter darkness.

Several lava flows spread across the surrounding land. Fifty seven people were killed, and over a billion dollars was caused in damage. Vast swaths of forest around the mountain were leveled by the furious wind or lava. The volcano erupted several other times, but never again to the same extent. The USGS is presently monitoring the area closely after several indicators that it may be reawakening.

There are, of course, many other instances of volcanos and eruptions of said volcanoes in the U.S. and certainly around the world. However, these are the most impactful occurrences to have shaken the country and its interests in recent history. Of course, that is only history. With Kilauea volcano currently erupting, Yellowstone, Cleveland, and Mount St. Helens are expected to erupt in the coming years, and if they do, it could have devastating consequences.