On May 18, 1980, a major volcanic eruption occurred on Mount St Helens in the US state of Washington. The blast, which measured 5 on the Volcanic Explosively Index, has been declared as the most disastrous volcanic eruption in modern US history. An eruption column rose 80,000 feet into the atmosphere and deposited ash in 11 states.
At least 57 people were killed and hundreds of square miles were reduced to wasteland, causing over $1billion (£770million) in damage.
However, many residents did not know the volcano had erupted until it was too late, it was revealed during a bombshell documentary.
Amazon Prime’s “Mega Disaster: It’s Happened Before, It Will Happen Again” series revealed how a “silent zone” prevented locals from having any idea their lives were at risk.
Geophysicist Keith Ronnholm revealed on the 2006 series: “I was reading a book in my car, when I heard some people yelling and looked over to the mountain.
“The entire north side of the mountain was sliding down.
“There was a puff of dark, grey ash and within 10 to 15 seconds, that ash expanded out and covered the entire mountain.
“All of this happened silently and there was no noise to reinforce my flight response.”
Mr Ronnholm detailed exactly how the volcano went unnoticed to so many and how it could happen again.
He added: “Because of the way the temperature is structured and the atmosphere gets cooler with height, the sound waves from explosions are bent away from the surface of the Earth.
“When they reach the stratosphere and the temperature increases they are bent back down.
“So no one from six to 60 miles from Mount St Helens heard the eruption.”
Since 1980, the mountain has experienced tens of thousands of small earthquakes and numerous minor eruptions.
Most notably, as of 2004, the volcano has been continuously erupting lava, which has created a large dome that is still growing.
Volcanologists, including Rick LaHusen of the United States Geological Survey (USGS), revealed the volcano could and probably will erupt again.
It is Mr LaHusen’s job to constantly monitor changes in activity.