US Forest Service

Mount St. Helens

Mount St. Helens National Monument

Mount St. Helens
Pacific Northwest Research Station
1220 SW 3rd Ave.
Portland, OR 97204

(503) 808-2100

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(FAQ 7) How were large mammals affected by the eruption?

Elk did not survive the blast, but these highly mobile animals were visiting the disturbed area within weeks after the eruption. During late summer, herds of adult bull elk travel together. Here they are running across the debris avalanche deposit (photo by Chuck Tonn).


Several large mammals lived in the Mount St. Helens area before the 1980 eruption. These included large herds of majestic elk (Cervus elaphus), black-tailed deer (Odocoileus hemionus columbianus), mountain goat (Oreamnos americanus), American black bear (Ursus americanus), and cougar (Puma concolor). The eruption’s devastating lateral blast and debris avalanche instantly killed all large animals, which could not outrun the flying rock and hot gases and were too big to hide. During search-and-rescue missions in the first few days after the eruption, emergency personnel saw many elk carcasses throughout the blowdown zone. Elk and other large animals survived in the tephra-fall zone where only cool ash and pumice buried the forest floor, but the animals were likely temporarily displaced as they searched for food.


Many large mammals are highly mobile and within days of the eruption traveled into the disturbed areas in search of food, which was initially in very low supply. Because these animals have large energy reserves and can travel long distances, they could afford to roam the disturbed areas, searching for food in the isolated vegetation patches.


Eruption’s effect on elk and deer

Herbivores, or plant-eating species, such as elk and deer returned to the blast area the first summer. They influenced the growth and spread of plants in several ways, some positive and some negative. First, these hoofed animals broke up the ash surface, which promoted erosion on steep slopes, thus allowing buried plants to sprout. Second, elk and deer tracks collected wind-blown seeds that later sprouted. Third, elk and deer carried seeds and spores in their gut track and later deposited the seeds and spores with their fecal material in the disturbed area. Negative effects included grazing, which severely affected developing vegetation on the pyroclastic flow, debris avalanche deposit, and blowdown zones. Elk spread the seeds of exotic plant species as well as native plants, and some exotic plants have spread quickly and displaced native species.

Elk herds flourished in the years after the eruption because highly nutritious leafy plants became increasingly abundant, the area was closed to hunting, and a string of mild winters favored high survival and good calving success. Elk populations reached several hundred animals within 5 years of the 1980 eruption and continued to increase until heavy snows in 1999 caused a substantial winter die-off. Since 1999, the number of elk has increased. Much of the area immediately north and west of the volcano remained closed to hunting through 2005.
Outside Mount St. Helens National Volcanic Monument, adjacent lands were salvage logged and planted with conifer seedlings after the 1980 eruption. As these conifers grow into young forests, shading out the forage that elk and deer prefer, these animals are likely to spend more time grazing in the monument, which still has many open areas because no trees were planted and natural succession is allowed to take place.

Eruption’s effect on mountain goats

In 1980, mountain goats may have survived on the south side of the volcano where the eruption had a minimal impact. The first reliable sighting of mountain goats on Mount St. Helens, however, occurred 7 years after the eruption. Since 1987, scientists have seen mountain goats on the volcanic cone. In 2000, scientists observed mountain goat tracks and fur in the volcano’s crater and, during summer 2003, scientists routinely saw a mountain goat at the base of Forsyth Glacier on the volcano’s north side.

Eruption’s effect on black bears

Black bears had little reason to venture into the blast area for several years after the eruption as little food was available for them. However, as young conifers grew and berry-producing plants became more abundant, black bears were routinely observed in the blowdown zone foraging on conifer bark and berries.

Eruption’s effect on cougars

Cougars, also known as mountain lions, are elusive animals that are highly secretive and difficult to observe. Scientists have spotted the remains of cougar kills and have seen cougar tracks in mud along lakes and streams in the blast area, leaving little doubt that these large cats are hunting deer, elk, and other animals in the blast area.

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US Forest Service - Pacific Northwest Research Station
Last Modified: Thursday,14May2015 at13:56:27CDT

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