Mount St. Helens: Cascades' restless giant

• Prior to the eruption, magma intrusion caused a massive bulge to form on the north flank.
• On May 18, 1980, a magnitude 5.1 earthquake triggered the collapse of the north flank, unleashing a 23-square-mile landslide.
• A lateral explosion followed, shooting hot gas, ash, and rock 15 miles into the sky and blanketing the region in an apocalyptic-like fallout of ash and debris.

By the numbers: Ash spread across at least 11 states and grounded more than 1,000 flights, per USGS.

• 230 square miles of forest were destroyed.
• The blast lowered the mountain's summit by 1,300 feet.

The bottom line: Mount St. Helens is not just history; it remains the most active volcano in the Cascades.

• Scientists are closely tracking it for seismic activity, magma accumulation and other signals of eruption.