Scientists measure volcanic eruptions by the amount of material that a volcano ejects into the atmosphere. Based on this measurement system, the largest eruptions include (in descending order of strength) one at Yellowstone Park in the United States, c. 600,000 B.C.; another at Toba, Indonesia, about 74,000 B.C.; a Tambora, Indonesia, eruption in A.D. 1815; Santorini, Greece, in 1470 B.C.; Laki, Iceland, in A.D. 1783 (which also produced the largest known lava flow in recorded history); and another in Indonesia, at Krakatau, in A.D. 1883.

The eruption in Yellowstone is hard to fathom: The volcano (which would have been located in present-day Wyoming) left a crater that measures 30 by 45 miles and released about 10,000 cubic kilometers of material into the atmosphere. To put this into perspective, consider that the next largest eruption, that at Toba, released one-tenth that amount, or 1,000 cubic kilometers. The one at Tambora released one-tenth of the Toba amount, 100 cubic kilometers. All of the others released about 10 cubic kilometers of earth debris into the atmosphere.

The May 18, 1980, eruption of Mount St. Helens in southwestern Washington State is also considered among the largest known eruptions in history and is the largest eruption in the modern history of the 48 contiguous Unites States. Mount St. Helens released a comparatively small amount of material, one cubic kilometer, but the damage was great after the volcano erupted. Much of the region was blanketed in ash, miles of forest were devastated, and the North Fork of the Toutle River was laden with ash and other volcanic debris up to 600 feet deep. The eruption claimed 57 lives.