US Forest Service

Mount St. Helens

Mount St. Helens National Monument
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Mount St. Helens
Pacific Northwest Research Station

333 SW First Avenue
Portland, OR 97204

(503) 808-2592

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Frequently Asked Questions


(FAQ 9) How were reptiles affected by the eruption?

The climate in the Mount St. Helens region is cool and wet, not conducive to most reptiles. Only four species of reptiles were likely to be found in the area before the eruption: three snakes and one lizard.

In the first few years after the 1980 eruption, scientists observed only one snake species, the common garter snake (Thamnophis sirtalis), and it appeared to be uncommon. Because the volcanic blast leveled the forest and left the former forest floor flooded with sunlight and buried by well-drained volcanic material, creating a somewhat warmer and drier environment, scientists predicted that reptiles would become more abundant in a few years. In fact, about 10 years after the eruption the number of common garter snakes increased dramatically, concentrated around lakes and streams at Mount St. Helens where the garter snakes prey heavily on amphibians. No other snake species has been documented in the area since the eruption, but several confirmed sightings of the northern alligator lizard (Elgaria coerulea) have been made.

As forest cover reclaims the landscape, keeping the ground cool and moist, scientists expect reptiles to become less abundant. This change will likely take several decades.


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US Forest Service - Pacific Northwest Research Station - Mount St. Helens
Last Modified:  Thursday, 28 March 2013 at 14:15:24 CDT

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