MOUNT ST HELENS
INTRODUCTION - TYPES OF VOLCANOES

VOLCANOES MADE OF 'RUNNY' LAVA - HAWAII

VOLCANOES MADE OF 'RUNNY' LAVA - GALAPAGOS

VOLCANOES MADE OF EXPLODED SOLIDS (TEPHRA)

VOLCANOES - MADE OF LAVA AND SOLIDS

INTRODUCTION - TYPES OF MATERIALS

RUNNY LAVA

RUNNY LAVA

PASTY LAVA

ASH

LAPILLI

BOMBS AND BLOCKS

WELDED ASH (IGNIMBRITE)

THE MAY 18, 1980 CATASTROPHIC ERUPTION
OF
MT. ST. HELENS

BEFORE

AFTER

SETTING, PREVIOUS HISTORY, PRECURSOR EVENTS

THE CASCADE RANGE

AFTER 123 YEARS QUIET, MARCH 20 QUAKES. ONE WEEK LATER, PHREATIC EXPLOSIONS

MAGMA RISE WITHIN MT -> 450' BULGE BY MAY 17.

THE CATASTROPHIC EVENTS OF MAY 18, 1980

8:32 AM: M= 5.1 QUAKE; GIANT LANDSLIDE, MAJOR PUMICE AND ASH ERUPTION. 1300 FEET OF PEAK COLLAPSED OR BLEW OUTWARD, DEBRIS AVALANCHE, LAHARS

FOUR SEQUENTIAL LANDSLIDE IMAGES:

LANDSLIDE DEPOSITS

DEBRIS AVALANCHE DEPOSITS

PYROCLASTIC FLOW

NINE HOUR VIGOROUS ASH PLUME ERUPTION.

ASH DEPOSITS

VOLCANIC ASH

CLEANING UP.

MAP OF ASH DISTRIBUTION

EFFECT OF LATERAL BLAST

FOREST DESTRUCTION - BEFORE

FOREST DESTRUCTION - AFTER

MUD FLOWS (LAHARS)

CRATER GLACIER - SOURCE OF WATER FOR LAHAR

LAHAR

HOUSE ENGULFED BY LAHAR

MAILBOX ENGULFED BY LAHAR

LAHAR - DEPTH OF MUD

PYROCLASTIC FLOW

PUMICE BLOCKS AT EDGE OF PYROCLASTIC FLOW

SUBSEQUENT EVENTS

FIVE MORE EXPLOSIVE ERUPTIONS IN 1980

1982 ERUPTION FOLLOWED BY LAHAR

DOME GROWTH AND DRAINAGE DEVELOPMENT

DOME GROWTH

HAZARD ABATEMENT

ON THE SCALE OF THINGS

MONITORING NETWORKS

MEASURING DOME GROWTH

ESTABLISHING SEISMIC STATION NEAR DOME

COLLECTING GAS SAMPLES

MEASURING CRACKS IN CRATER FLOOR

REMOTE MONITORING STATIONS

LAKES DAMMED BY DEBRIS FLOW

FLOOD GAGES TO WARN OF DAM FAILURE

OUTLET CHANNELS

RIVER CHANNEL SEDIMENTATION

DREDGING

SEDIMENT RETENTION DAM

LIFE RETURNS

EVENTS OF OCTOBER, 2004

VISITOR OBSERVATION PLATFORM

DOME UPLIFT

PHREATIC EXPLOSIONS FROM DOME

CRATER ASH ERUPTION

ASH FALL ON CRATER FLOOR

DEBRIS FLOW CLOGS RIVER CHANNEL

WHAT'S GOING ON?

BEFORE

AFTER

ARCHITECTURE, PROCESS AND MATERIALS

SUBDUCTION ZONE

TRIGGERING EVENTS

A, The volcano in the early morning of May 18, 1980; the bulging of the north flank is clearly shown by the pre-1980 and pre-collapse profiles.

B and C, (within about 30 seconds after the collapse) show the progressive development of the debris avalanche and the beginning of both the lateral blast and vertical eruption, as the cryptodome was exposed; the Bulge block was the first to slide, followed by the Graben block.

D, (about another 30 seconds later), by now the Summit block had slid and the lateral blast had stopped; the vertical eruption was now in full fury.

ERUPTIVE MECHANISMS

SUMMARY OF EVENTS

©2004
David Leveson