Photos: Mt. St. Helens erupts 40 years ago, killing 57 people

Mount St. Helens sends a plume of ash, smoke and debris skyward in its most violent eruption to date, May 18, 1980. The volcano, located 45 miles northeast of Portland, Wash., became active on March 27. Flooding in some areas has been triggered by the volcano and residents have been evacuated. (AP Photo/Jack Smith)
A large crater can be seen at left as Mount St. Helens erupts, April 2, 1980, spewing black smoke and ash skyward. Mount St. Helens is located 45 miles northeast of Portland in Washington. (AP Photo/Jack Smith)
Theresa Temple, a student at Portland State University walks to her morning classes with a mask on to protect her from breathing the ash that fell in Portland from Mt. St. Helens, Oct. 17, 1980. The volcano which is located 45 miles northeast of Portland, Ore., erupted late Thursday night and early Friday morning, sending ash in a southwesterly direction. (AP Photo/Eric Risberg)
This area near Spirit Lake at the base of Mount St. Helens takes on a new moon-like form following the eruption and massive mud flows of from Mount St. Helens, Tuesday, May 20, 1980 in Washington state. At least six persons are dead and many more missing. (AP Photo)
Residents stop and try to remember how the Old 99 Steelhead Drive near Longview used to look before the mud and logs started to cover it from the eruption of Mt. St. Helens, some 50 miles away, May 20, 1980. At least six people are dead and about 100 missing. (AP Photo/Sal Veder)
Ransom Tew, 71, of Portland, Ore., wears a protective surgical mask as he waits for the light in downtown Portland, May 26, 1980. Ash from Mount St. Helens blanketed the city causing some discomfort and snarling traffic. (AP Photo/Gary Stewart)
Mount St. Helens, an active volcano located 45 miles northeast of Portland, Wash., vents a cloud of ash and steam, May 24, 1980. The mountain has been generally quiet except for an occasional eruption. (AP Photo)
Volcanic ash, on August 11, 1980, from Mount St Helens magnified 200 times by a Sperry-Rand scanning electron microscope at NASA's Goddard Space Flight Centre in Greenbelt, Maryland. (Photo by NASA/Hulton Archive/Getty Images)
Mount St. Helens erupts with black smoke and ash providing a spectacular sight as the cloud drifted skyward, March 30, 1980. Mount St. Helens is located about 45 miles northeast of Portland. The 9,677-foot peak had been a dormant volcano for more than a century until several days ago. (AP Photo/Jack Smith)
Smoke, ash and debris spew skyward as Mount St. Helens erupts, May 19, 1980 sending a plume more than nine miles into the air. At least seven deaths have been attributed to the volcano which is located 45 miles northeast of Portland, Washington. (AP Photo/Jack Smith)

May 18, 2020 at 12:42 p.m.

CLICK HERE if you are having a problem viewing the photos on a mobile device

“On May 18, 1980 the eruption of Mount St. Helens became the deadliest and most economically destructive volcanic event in U.S. history. (A total of) 57 people died and thousands of animals were killed. Hundreds of homes and miles of railways and highway were destroyed,” according to U.S. Geological Survey Fact Sheet 036-00.

“The first sign of activity at Mount St. Helens in the spring of 1980 was a series of small earthquakes that began on March 16. After hundreds of additional earthquakes, steam explosions on March 27 blasted a crater through the volcano’s summit ice cap. Within a week the crater had grown to about 1,300 feet in diameter and two giant crack systems crossed the entire summit area. By May 17, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward at least 450 feet to form a noticeable bulge. Such dramatic deformation of the volcano was strong evidence that molten rock (magma) had risen high into the volcano.

“Within 15 to 20 seconds of a magnitude 5.1 earthquake at 8:32 a.m.on May 18, 1980, the volcano’s bulge and summit slid away in a huge landslide – the largest on Earth in recorded history. The landslide depressurized the volcano’s magma system, triggering powerful explosions that ripped through the sliding debris. Rocks, ash, volcanic gas, and steam were blasted upward and outward to the north. This lateral blast of hot material accelerated to at least 300 miles per hour, then slowed as the rocks and ash fell to the ground and spread away from the volcano; several people escaping the blast on its western edge were able to keep ahead of the advancing cloud by driving 65 to 100 miles an hour! The blast cloud traveled as far as 17 miles northward from the volcano and the landslide traveled about 14 miles west down the North Fork Toutle River.

“The lateral blast produced a column of ash and gas (eruption column) that rose more than 15 miles into the atmosphere in only 15 minutes. Less than an hour later, a second eruption column formed as magma erupted explosively from the new crater. Then, beginning just after noon, swift avalanches of hot ash, pumice, and gas (pyroclastic flows) poured out of the crater at 50 to 80 miles per hour and spread as far as 5 miles to the north. Based on the eruption rate of these pyroclastic flows, scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m. Over the course of the day, prevailing winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 250 miles from the volcano.

“During the first few minutes of this eruption, parts of the blast cloud surged over the newly formed crater rim and down the west, south, and east sides of the volcano. The hot rocks and gas quickly melted some of the snow and ice capping the volcano, creating surges of water that eroded and mixed with loose rock debris to form volcanic mudflows (lahars). Several lahars poured down the volcano into river valleys, ripping trees from their roots and destroying roads and bridges.

“The largest and most destructive lahar was formed by water seeping from inside the huge landslide deposit through most of the day. This sustained flow of water eroded material from both the landslide deposit and channel of the North Fork Toutle River. The lahar increased in size as it traveled downstream, destroying bridges and homes and eventually flowing into the Cowlitz River. It reached its maximum size at about midnight in the Cowlitz River about 50 miles downstream from the volcano.”