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Explosive eruptions
Gas-rich magma can produce powerful ash columns and blasts.
Volcano profile · Washington, USA
Mount
St. Helens
The Cascade volcano whose 1980 collapse, lateral blast and ash column transformed the landscape — and changed volcanic hazard science worldwide.
Latest activity and alert level
Check the live status hub
Mount St. Helens is continuously monitored and conditions can change over time. View the Volcoholics volcano directory for the latest verified official position from USGS Cascades Volcano Observatory.
View latest Mount St. Helens status →America's most famous volcano
A mountain rebuilt after catastrophe
Mount St. Helens is the most active volcano in the Cascade Range and one of the world's best-studied volcanic systems.
The 18 May 1980 eruption removed the upper 400 metres of the mountain, opened a vast horseshoe-shaped crater to the north and produced a debris avalanche, lateral blast, pyroclastic flows, ashfall and lahars.
The volcano did not stop there. Lava domes grew during 1980–1986 and again during 2004–2008, while Crater Glacier developed around them inside the new crater.
2,549 mElevation
StratovolcanoVolcano type
Horseshoe craterDefining feature
2004–2008Latest eruption
St. Helens quick facts
- Volcano type
- Explosive dacite stratovolcano
- Location
- Cascade Range, Washington
- 1980 eruption
- VEI 5
- Crater
- 2 × 3.5 km, open north
- Official agency
- USGS CVO
Activity and behaviour
Quiet at the surface, intensely monitored below
Evergreen profile
How Mount St. Helens behaves
Mount St. Helens can alternate between long quiet intervals, earthquake swarms, magma intrusion, dome growth and explosive eruption. Its 1980 sector collapse reshaped both the mountain and modern volcanology.
Check the latest verified status →Volcano typeStratovolcanoSteep-sided and capable of explosive eruption
Defining featureHorseshoe craterCreated by the 1980 landslide and lateral blast
Modern activityDome growthRepeated lava-dome building has occurred since 1980
Main hazardsBlast, ash and laharsHazards vary by eruption style and direction
Official sourceUSGS CVOAuthoritative monitoring and hazard guidance
The defining eruption
The mountain that changed overnight
The 1980 catastrophe was not a simple vertical explosion. It began with structural failure and unfolded in minutes.
01
North flank bulges
A shallow cryptodome pushes the north flank outward.
02
M5.1 earthquake
Shaking removes support from the unstable bulge.
03
Debris avalanche
The summit and north flank collapse in a vast debris avalanche.
04
Lateral blast
Pressure escapes sideways in a devastating northward blast.
05
Plinian eruption column
Ash and gas rise high after the magma system is exposed.
06
Lahars
Meltwater and volcanic debris surge down river valleys.
Duration: minutes.
The processes overlapped in reality; the sequence is separated here for clarity.
Inside the volcano
How Mount St. Helens works
Viscous dacite magma rises through a steep volcanic edifice and may accumulate as lava domes.
Dacite magmaGas-rich and resistant to flow.
Shallow storagePressure changes drive unrest.
Lava domesViscous lava rebuilds the crater floor.
Hydrothermal alterationHot fluids weaken rock and shape hazards.
A mountain open to the north
The horseshoe crater
The landslide removed the summit and northern flank, leaving a crater unlike the volcano's pre-1980 cone.
Inside it, lava domes from two eruptive periods occupy only a fraction of the missing volume, while one of North America's youngest glaciers has grown around them.
Monitoring
Watching recovery and recharge
CVO watches earthquakes, deformation, gas, heat, ice and surface change to distinguish normal background activity from renewed unrest.
Seismic networkTracks earthquakes and tremor.
GNSS and tiltMeasure ground deformation.
Gas surveysTrack carbon dioxide and sulphur dioxide.
WebcamsWatch crater and weather conditions.
Satellite dataMap heat and broad deformation.
Field scienceStudies glacier, domes and altered rock.
A volcano through time
Mount St. Helens eruption timeline
~40,000 years
Ancestral volcano develops
Multiple eruptive stages build the complex volcano known today.
1480s
Goat Rocks eruptive period
Large explosive eruptions and dome growth reshape the summit.
1800–57
Goat Rocks dome and historical activity
Explosions and lava extrusion mark the last activity before the twentieth century.
20 Mar 1980
Earthquake swarm begins
Unrest rapidly escalates, followed by steam explosions and growth of the north-flank bulge.
Catastrophic eruption18 May 1980
Landslide, lateral blast and ash column
The summit and north flank collapse, triggering the defining eruption and killing 57 people.
1980–86
First post-eruption lava dome
Repeated extrusion partly rebuilds the crater floor.
Latest eruption2004–08
Renewed dome growth
Spine-like lava extrusion adds roughly the same volume as the 1980–86 dome-building period.
Present
Normal background monitoring
The volcano remains active, quiet and closely watched.
What matters most
Mount St. Helens' main hazards
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Pyroclastic density currents
Hot ash, gas and rock can move rapidly across the ground.
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Lahars
Water, snow and volcanic debris can surge far down river valleys.
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Ashfall
Ash can affect communities, agriculture, transport and aviation.
Volcoholics InsightThe next eruption does not have to repeat 1980. Hazard planning must cover many eruption sizes, directions and combinations.
Myths and reality
Mount St. Helens myths, separated from the science
The volcano simply “blew its top”.
Reality: a huge landslide removed support and triggered the lateral blast.
Mount St. Helens is extinct now.
Reality: it erupted again from 2004 to 2008 and remains active.
The next eruption will copy 1980.
Reality: future activity could range from dome growth to smaller or differently directed explosions.
The crater is empty.
Reality: it contains two lava domes, a glacier and an active hydrothermal system.
A mountain permanently changed
1980: Before and after
The eruption removed the summit and north flank, lowered the mountain by roughly 400 metres and opened the horseshoe crater seen today.
Questions answered
Mount St. Helens explained
Is Mount St. Helens erupting now?
No. It is currently at official monitoring, with background activity.
When was its last eruption?
The latest eruptive period lasted from 2004 to 2008 and built a new lava dome.
What caused the 1980 lateral blast?
Collapse of the unstable north flank suddenly removed pressure from shallow magma, releasing a powerful horizontal blast.
Why is the crater open to the north?
The 1980 debris avalanche removed the summit and northern side of the volcano.
Could Mount St. Helens erupt again?
Yes. It remains an active volcano, although there are currently no signs of an imminent eruption.
Official science, made readable
Built from the agencies watching Mount St. Helens
Operational status belongs to the USGS Cascades Volcano Observatory. Volcoholics provides context and never replaces official warnings.