Summary Table
| Eruption summary May 18, 1980, eruption of Mount St. Helens |
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|---|---|---|
| Volcano | Elevation of summit: | Before eruption: 9,677 ft (2,950 m) After eruption: 8,363 ft (2,549 m) Total removed: 1,314 ft (401 m) |
| Crater dimensions: | East-West: 1.2 mi (1.9 km) North-South: 1.8 mi (2.9 km) Depth: 2,084 ft (635 m) |
|
| Crater floor elevation: | 6,279 ft (1,914 m) | |
| Eruption | Date: | May 18, 1980 |
| Time of initial blast: | 8:32 a.m. Pacific Daylight Time (UTC−7) | |
| Eruption trigger: | A magnitude 5.1 earthquake about 1 mi (1.6 km) beneath the volcano | |
| Landslide and debris avalanche |
Area covered: | 23 sq mi (60 km2) |
| Volume: |
0.67 cu mi (2.8 km3) | |
| Depth of deposit: | Buried North Fork Toutle River to average depth of 150 ft (46 m) with a maximum depth of 600 ft (183 m) | |
| Velocity: | 70 mph (113 km/h) to 150 mph (241 km/h) | |
| Lateral blast | Area covered: | 230 sq mi (596 km2); reached 17 mi (27 km) northwest of the crater |
| Volume of deposit: |
0.046 cu mi (0.19 km3) | |
| Depth of deposit: | From about 3 ft (1 m) at volcano to less than 1 in (2.5 cm) at blast edge | |
| Velocity: | At least 300 mph (483 km/h) | |
| Temperature: | As high as 660 °F (349 °C) | |
| Energy release: | 24 megatons thermal energy (7 by blast, rest through release of heat) | |
| Trees blown down: | 4,000,000,000 board feet (9,400,000 m3) of timber (enough to build about 300,000 two-bedroom homes) | |
| Human fatalities: | 57 | |
| Lahars | Velocity: | About 10 mph (16 km/h) to 25 mph (40 km/h) and over 50 mph (80 km/h) on steep flanks of volcano |
| Damaged: | 27 bridges, nearly 200 homes. Blast and lahars destroyed more than 185 mi (298 km) of highways and roads and 15 mi (24 km) of railways. | |
| Effects on Cowlitz River: | Reduced carrying capacity at flood stage at Castle Rock from 76,000 cu ft (2,200 m3) per second to less than 15,000 cu ft (420 m3) per second. | |
| Effects on Columbia River: | Reduced channel depth from 40 ft (12 m) to 14 ft (4 m); stranded 31 ships in upstream ports | |
| Eruption column and cloud |
Height: | Reached about 80,000 ft (24,400 m) in less than 15 minutes |
| Downwind extent: | Spread across U.S. in 3 days; circled Earth in 15 days | |
| Volume of ash: |
0.26 cu mi (1.1 km3) | |
| Ash fall area: | Detectable amounts of ash covered 22,000 sq mi (57,000 km2) | |
| Ash fall depth: | 10 in (25 cm) at 10 mi (16 km) downwind (ash and pumice) 1 in (2.5 cm) at 60 mi (97 km) downwind 0.5 in (1.3 cm) at 300 mi (482.8 km) downwind |
|
| Pyroclastic flows | Area covered: | 6 sq mi (16 km2); reached as far as 5 mi (8 km) north of crater |
| Volume and depth: |
0.029 cu mi (0.12 km3); multiple flows 3 ft (1 m) to 30 ft (9 m) thick; cumulative depth of deposits reached 120 ft (37 m) in places | |
| Velocity: | Estimated at 50 mph (80 km/h) to 80 mph (130 km/h) | |
| Temperature: | At least 1,300 °F (700 °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. | |
| Brantley and Myers, 1997, Mount St. Helens – From the 1980 Eruption to 1996: USGS Fact Sheet 070–97, accessed 2007-06-05; and Tilling, Topinka, and Swanson, 1990, Eruption of Mount St. Helens – Past, Present, and Future: USGS General Interest Publication, accessed 2007-06-05. | ||
| Table compiled by Lyn Topinka, USGS/CVO, 1997 | ||
Read more about this topic: 1980 Eruption Of Mount St. Helens
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