LAKE CLARK

NATIONAL PARK

AND WILDERNESS

BOUNDARY

(approximate)

L3

L3

L3

L2

L3

L1

L1

L2

L3

100

100

100

100

100

500

500

500

500

500

500

500

500

500

500

500

1000

1000

1000

1000

1500

1500

2000

2500

153o00' 153o

30'

60o

15'

60o

00'

0 5

0 5 10 KILOMETERS

MILES

Red 

Glacier

COOK INLET

CHINITNA BAY

TUXEDNI BAY

Crescent River

Tuxedni Glacier

Tuxedni 

River

River

Johnson

River

Creek

West

Glacier

ILIAMNA

VOLCANO

CHISIK

ISLAND

Red Creek

Silver Salmon

Glacier

Lateral

Umbrella

Glacier

Areas likely to be inundated by lahars (volcanic debris flows), lahar-runout flows, and floods 

during most eruptions.

Areas susceptible to inundation by lahars, lahar-runout flows, and floods during most eruptions 

but less likely to be affected than zone L1.

Areas that could be inundated by lahars, lahar-runout flows, and floods during large sustained 

eruptions but less likely to be affected than zones L1 or L2.

Probable extent of a debris avalanche from Iliamna Volcano for H/L = 0.2 (see discussion in text)

Probable extent of a debris avalanche from Iliamna Volcano for H/L = 0.4 (see discussion in text) 

Extent of pyroclastic flows for H/L = 0.2 (see discussion in text). Pyroclastic flows associated 

with eruption-column collapse could extend to about this boundary during moderate to large 

eruptions. This boundary is only approximate and is not based on known pyroclastic-flow deposits. 

More likely are pyroclastic flows associated with collapsing lava domes that would be directed 

over dicrete sectors of the volcano and along major valleys.

Most likely flow paths for pyroclastic flows and surges. During moderate to large eruptions,

pyroclastic flows and surges could be directed along topographically low areas such as valleys 

and drainages and could extend beyond the hazard-zone boundary defined by H/L = 0.2 (see 

discussion in text).

Extent of area that could be affected by a directed blast similar to the blast generated during the 

1980 eruption of Mt. St. Helens, Washington. This hazard boundary is a worst-case condition for 

Iliamna Volcano. If a directed blast were to occur, it could engulf as much as a 180 degree sector 

of the indicated hazard zone.

Fumaroles (gas vents)

Zone of hydrothermally altered bedrock

L1

EXPLANATION

L2

L3

LAHAR HAZARDS

DEBRIS AVALANCHE HAZARDS

PYROCLASTIC FLOW AND SURGE HAZARDS

LATERAL BLAST HAZARDS

The preliminary hazard-zonation map indicates generalized hazardous areas associated with future 

eruptions of Iliamna Volcano either from a summit vent or flank vent on the modern edifice. Also 

indicated are areas at risk from various volcano-related events such as debris avalanche and lahar 

that may not be related to an actual eruption. Pyroclastic eruptions are likely to initiate lahars and 

floods and will probably result in variable amounts of ashfall. Debris avalanches and combination 

snow-ice-rock avalanches can occur at any time but are unlikely to be hazardous except to someone 

on upper Red, Umbrella, Lateral, or Tuxedni Glaciers. Historical avalanches have not transformed 

to lahars but a large flank collapse could evolve to a lahar that would inundate downstream valleys.

The hazard-zone boundaries do not indicate a major change in the degree of hazard but are generalized approximations based on known deposits and eruptive characteristics of similar volcanoes. The 

degree of hazard generally decreases in a downvalley direction and as height above the valley floor 

increases.

NOTE ABOUT VOLCANO HAZARD-ZONE BOUNDARIES

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

VOLCANIC ASH HAZARDS

The hazard zone for volcanic ash is likely to be similar to the extent of ash fallout of recent eruptions 

of other Cook Inlet volcanoes. The specific area of ash fallout depends on the prevailing winds, which

are generally from the west. Ash plumes could rise to 12,000 meters altitude and would drift downwind as ash clouds for days to weeks following an eruption. Drifting clouds of volcanic ash would be 

hazardous to all aircraft in areas downwind from the volcano.

Red 

Contour interval in meters

PRELIMINARY VOLCANO-HAZARD ASSESSMENT FOR ILIAMNA VOLCANO, ALASKA

by

Christopher F. Waythomas and Thomas P. Miller

1999

OPEN-FILE REPORT 99-373

PLATE 1

FAIRBANKS

JUNEAU

ILIAMNA 

VOLCANO

Area likely to be affected

by ash fallout during a

future eruption

KODIAK

HOMER

SITKA

TALKEETNA

ANCHORAGE

USGS - UAF/GI - ADGGS

Ala

ska Volcano Observato

r

y