On May 18, 1980, Mount St. Helens in Washington State erupted in the most explosive volcanic event in United States history. Fifty-seven people and countless animals died, a forest was leveled, and ash blanketed the region as far away as Minnesota.

The volcano remains active today, even as events are being held at the mountain to mark the 36th anniversary of the disaster. Since mid-March, the U.S. Geological Survey has detected a swarm of 130 earthquakes in the surrounding area, suggesting that magma is on the move below the surface. The latest activity is part of a series of changes recorded at the stratovolcano since the dramatic eruption.

That blast ejected 1,300 feet (396 meters) of rock, excavating a massive crater and causing the biggest avalanche in U.S. history. (See pictures before and after the disaster.)

Among the casualties was a herd of mountain goats that had been prized by tourists and people who collected their wool for weaving. The goats have returned over the past few years, with an estimated population at more than a hundred.

Similarly, trees are returning to an area that had been blasted to a moonscape, giving scientists a rare opportunity to study the ways plants and animals colonize a ravaged landscape. (Read about the changes 30 years after the eruption.)

Hiking is once again allowed on the mountain, and an observatory provides a unique look into the crater. Scientists hope their constant monitoring can provide enough of a warning for an evacuation if another eruption is imminent.

Proving that it still has power, over the past few years, Mount St. Helens has had "a baby volcano growing in its crater," says Stephanie Grocke, a volcanologist at the Smithsonian Institution and a National Geographic explorer.

Between 2004 and 2008, enough molten rock oozed out of the crater to pave a seven-lane highway from New York City to Portland, Oregon, notes Grocke. As such, the mountain remains a dangerous threat.

"The volcano is still living and breathing," says Grocke.