Before 1980, Mount St. Helens, in Washington, was just another volcano in the Ring of Fire.
That's the huge circle of volcanoes that ring the Pacific Ocean.
The volcano had not erupted in over a hundred years.
It was green and rich with wildlife.
Spirit Lake, below the mountain, was full of fish and plants.
But then this volcano woke up!
Hot melted rock, called magma, had created lots of gas deep underground.
This gas had built up, causing pressure within the volcano.
On May 18, 1980, an earthquake struck the area—and Mount St. Helens finally erupted.
When the volcano exploded, its entire north side collapsed.
This created the biggest landslide in modern history.
Lava, which is magma that has reached the surface, blasted out of the mountain.
The lava mixed with rock, ash, and melted snow.
It flowed over the landscape.
Clouds of hot gases and rocks burst out too.
They knocked down entire forests.
The violent eruption left a huge crater at the top of the mountain—nearly three kilometers wide.
Mount St. Helens was now four hundred meters shorter than before the eruption!
This wasn't the most serious damage.
Fifty-seven people died in the eruption.
Roads, bridges, and hundreds of homes were destroyed.
Right after the eruption, scientists began to study the scene.
Ash and volcanic rock covered most of the landscape.
Spirit Lake was filled with ash and rock too.
Broken trees covered the surface of the lake.
There was nothing alive in sight.
The entire area looked as lifeless as the moon!
Scientists believed decades would pass before animals and plants returned to the area.
Yet only three months later, scientists spotted something incredible.
A gopher was digging out of its tunnel!
The animal had stayed safe underground during the dangerous eruption.
By the next spring, a plant was growing!
After ten years, plants had grown back and animals had returned.
Plankton and plants filled Spirit Lake again.
Life had returned to the mountain.
Meanwhile the volcano hadn't exactly fallen back to sleep.
After the eruption, lava continued to build up at the crater's floor.
It rose and rose.
By 1986 the lava had formed a dome 270 meters high.
Then the mountain grew mostly quiet again.
Once in a while, the mountain rumbled.
There were even small explosions.
But none of this activity was very serious.
In 2004 ash and steam clouds rose once more from the crater.
Rocks as big as buildings pushed up from the crater floor.
What was happening now?
No one knew.
But by 2007 the mountain went back to sleep.
Scientists think that the volcano may have run out of gas.
Today earthquakes and rumblings continue to occur near Mount St. Helens.
The good news is that scientists have learned a lot since the 1980 eruption.
These lessons will help them to make better predictions about future eruptions.
No one knows exactly when Mount St. Helens will wake up again.
But when it does, people are more likely to be prepared.