Description

These illustrations show the landslide (green) and directed blast (red) that occurred during the first few minutes of the eruption of Mount St. Helens in 1980.

Before the eruption, an estimated 0.11 km³ of dacite magma had intruded into the volcano (equivalent to sphere about 600 m in diameter!). The rising magma forced the volcano's north flank (right side of illustration) outward about 150 m and heated the volcano's ground water system, causing many steam-driven explosions (phreatic eruptions).

Following a magnitude five earthquake on the morning of May 18, 1980, a landslide (green) unroofed the hot magma and surrounding hydrothermal system, and the resulting rapid depressurization caused a series of steam and volcanic gas driven explosions. The explosions burst through part of the landslide, blasting rock debris northward. The resulting pyroclastic surge quickly overran the landslide and spread over ridges and valleys across an area of 550 km².

USGS image (by T.R. Alpha) and text from [1]

Description

Conditions d’utilisation

Cette image est placée dans le domaine public parce qu'elle contient des éléments issus de l'United States Geological Survey, une agence du Département de l'Intérieur des États-Unis. Pour plus d'information, consultez la politique officielle de copyright de l'USGS (en anglais) Bahasa Indonesia ∙ català ∙ čeština ∙ Deutsch ∙ eesti ∙ English ∙ español ∙ français ∙ galego ∙ italiano ∙ Nederlands ∙ português ∙ polski ∙ sicilianu ∙ suomi ∙ Tiếng Việt ∙ Türkçe ∙ български ∙ македонски ∙ русский ∙ മലയാളം ∙ 한국어 ∙ 日本語 ∙ 中文 ∙ 中文（简体） ∙ 中文（繁體） ∙ العربية ∙ فارسی ∙ +/−