May 18, 1980 Eruption of Mount St. Helens - Eruption Summary
VOLCANO	Elevation of Summit:	9,677 feet before; 8,363 feet after; 1,314 feet removed
	Volume removed (based on uncompacted deposits):	0.67 cubic miles (3.7 billion cubic yards)
	Crater dimensions:	1.2 miles (east-west); 1.8 miles (north-south); 2,084 feet deep
	Crater floor elevation:	6,279 feet
ERUPTION	Date:	May 18, 1980
	Time of initial blast:	8:32 a.m. PDT
	Eruption trigger:	A magnitude 5.1 earthquake about 1 mile beneath the volcano
LANDSLIDE - DEBRIS AVALANCHE	Area and volume (volume based on uncompacted deposits):	23 square miles (0.67 cubic miles) (3.7 billion cubic yards)
	Depth of deposit:	Buried North Fork Toutle River to average depth of 150 feet (maximum depth 600 feet)
	Velocity:	70 to 150 miles per hour
LATERAL BLAST	Area covered:	230 square miles; reached 17 miles northwest of the crater
	Volume of deposit (based on uncompacted deposits):	0.046 cubic miles (250 million cubic yards)
	Depth of deposit:	From about 3 feet at volcano to less than 1 inch at blast edge
	Velocity:	At least 300 miles per hour
	Temperature:	As high as 660 degrees F (350 degrees C)
	Energy release:	24 megatons thermal energy (7 by blast, rest through release of heat)
	Trees blown down:	4 billion board feet of timber (enough to build about 300,000 two-bedroom homes)
	Human fatalities:	57
LAHARS	Velocity:	About 10 to 25 miles per hour (over 50 miles per hour on steep flanks of volcano)
	Damaged:	27 bridges, nearly 200 homes. Blast and lahars destroyed more than 185 miles of highways and roads and 15 miles of railways.
	Effects on Cowlitz River:	Reduced carrying capacity at flood stage at Castle Rock from 76,000 cfs (cubic feet per second) to less than 15,000 cfs
	Effects on Columbia River:	Reduced channel depth from 40 to 14 feet; stranded 31 ships in upstream ports
ERUPTION COLUMN AND CLOUD	Height:	Reached about 80,000 feet in less than 15 minutes
	Downwind extent:	Spread across U.S. in 3 days; circled Earth in 15 days
	Volume of ash (based on uncompacted deposits):	0.26 cubic miles (1.4 billion cubic yards)
	Ash fall area:	Detectable amounts of ash covered 22,000 square miles
	Ash fall depth:	10 inches at 10 miles downwind (ash and pumice); 1 inch at 60 miles downwind; 1/2 inch at 300 miles downwind
PYROCLASTIC FLOWS	Area covered:	6 square miles; reached as far as 5 miles north of crater
	Volume and depth (volume based on uncompacted deposits):	0.029 cubic miles (155 million cubic yards); multiple flows 3 to 30 feet thick; cumulative depth of deposits reached 120 feet in places
	Velocity:	Estimated at 50 to 80 miles per hour
	Temperature:	At least 1,300 degrees F (700 degrees C)
OTHER	Wildlife:	The Washington State Department of Game estimated nearly 7,000 big game animals (deer, elk, and bear) perished as well as all birds and most small mammals. Many burrowing rodents, frogs, salamanders, and crawfish, managed to survive because they were below ground level or water surface when the disaster struck.
	Fisheries:	The Washington Department of Fisheries estimated that 12 million Chinook and Coho salmon fingerlings were killed when hatcheries were destroyed. Another estimated 40,000 young salmon were lost when forced to swim through turbine blades of hydroelectric generators as reservoir levels along the Lewis River were kept low to accommodate possible mudflows and flooding.
-- From: Brantley and Myers, 1997, Mount St. Helens -- From the 1980 Eruption to 1996: USGS Fact Sheet 070-97 and Tilling, Topinka, and Swanson, 1990, Eruption of Mount St. Helens - Past, Present, and Future: USGS General Interest Publication
Table compiled by Lyn Topinka, USGS/CVO, 1997

Mount St. Helens