When did Mount Saint Hellens erupt?

Answer 1

The early eruptive stages of Mount St. Helens are known as the "Ape Canyon Stage" (around 40-35,000 years ago), the "Cougar Stage" (ca. 20-18,000 years ago), and the "Swift Creek Stage" (roughly 13-8,000 years ago).

A dormancy of about 4,000 years was broken around 2500 BCE with the start of the Smith Creek eruptive period, when eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles. An eruption in 1900 BCE was the largest known eruption from St. Helens during the Holocene epoch, judged by the volume of one of the tephra layers from that period. This eruptive period lasted until about 1600 BCE and left 18 inches (46 cm) deep deposits of material 50 miles (80 km) distant.

The next eruptive period, the Castle Creek period, began about 400 BCE, and is characterized by a change in composition of St. Helens' lava, with the addition of olivine and basalt. Another 400 years of dormancy ensued.

The Sugar Bowl eruptive period was short and markedly different from other periods in Mount St. Helens history. It produced the only unequivocal laterally directed blast known from Mount St. Helens before the 1980 eruptions.

Roughly 700 years of dormancy were broken in about 1480, when large amounts of pale gray dacite pumice and ash started to erupt, beginning the Kalama period. The eruption in 1480 was several times larger than the May 18, 1980, eruption. In 1482, another large eruption rivaling the 1980 eruption in volume is known to have occurred. St. Helens reached its greatest height and achieved its highly symmetrical form by the time the Kalama eruptive cycle ended, about 1647. A 57-year eruptive period started in 1800. There were at least a dozen reported small eruptions of ash from 1831 to 1857, including a fairly large one in 1842.

Mount St. Helens is most notorious for its catastrophic eruption on May 18, 1980, at 8:32 am PDT.

Answer 2

Mount St. Helens erupted on May 18, 1980. The eruption was one of the most catastrophic volcanic events in U.S. history, causing significant destruction and loss of life.