"Inland Brown Bear" by NPS Photo /W. Hill , public domain
Lake ClarkVolcanoes |
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Lake Clark
National Park Service
U.S. Department of the Interior
Lake Clark National Park and Preserve
www.nps.gov/lacl
Qizhjeh Vena
Redoubt steaming courtesy of Game McGimsey/ AVO/ USGS
Volcanoes
Lake Clark is a land of fre and ice, dominated by two active volcanoes and over
900 square miles of glaciers. The scene of a dynamic, active geology, this is a
young landscape that is ever-changing.
Why are the
Volcanoes Here?
Lake Clark’s two volcanoes sit on the AlaskaAleutian subduction zone. Here the denser
oceanic crust of the Pacifc Plate is moving
beneath the lighter continental crust of the
North American Plate at a rate of approximately
2.6 inches per year; about as fast as fngernails
grow. Located only 30 miles beneath the surface
of the Kenai Mountains, the Pacifc Plate dives
abruptly at the western edge of Cook Inlet,
reaching a depth of more than 60 miles beneath
the Chigmit Mountains. The intense heat and
pressure at that depth melt rock, creating the
magma which erupts to the surface forming
Redoubt and Iliamna volcanoes.
Redoubt courtesy of K.L. Wallace /AVO/USGS
Iliamna - 10,016 ft. tall
Iliamna courtesy of Dennis Anderson/AVO/USGS
These volcanoes are geologically young;
Redoubt began forming a mere 880,000 years
ago. However, igneous rock throughout the park
and preserve indicate volcanic activity has been
present in the area for 180 million years. Over
time the rock layers near today’s volcanoes were
uplifted and exposed creating the Chigmit and
Neacola Mountains.
Redoubt - 10,197 ft. tall
Subduction graphic adapted from AVO/USGS
At the head of the Alaska Peninsula the Neacola
and Chigmit Mountains link the Alaska Range
curving to the northeast with the Aleutian Range
stretching to the southwest. Towering above
them all are two stratovolcanoes composed of
layers of andesitic pyroclastic deposits and lava
fows. This lava was thick, sticky, and fowed
like cold honey. Eruptions here are not likely
to fow efusively like those of the Hawaiian
volcanoes, where gases can easily bubble out
like a pot of boiling spaghetti sauce. Instead
the gases trapped in the viscous magma create
dramatic eruptions that break the magma into
solid pieces of many diferent sizes ranging from
boulders to ash, and known as pyroclasts. Like a
popcorn popper flled with kernels and confetti,
the larger, heavier particles fall closer to the
volcano’s vent, while the smaller, lighter ones
travel further away, creating the classically tall,
conical shape.
Sunset by NPS/ E. Wasserman
Introducing
Lake Clark’s
Volcanoes
Earthquakes
and Volcanoes
Hundreds of earthquakes shake the area each
year. Scientists documented 10,400 earthquakes
at Redoubt alone between 1989 and 2010, most
of which were associated with the volcano’s
eruptions. Mapping “earthquake focus” is how
geologists determine both the location and
depth of the subducting plate and the storage
and movement of magma through a volcano’s
underground chambers. Understanding
earthquake character and timing may also lead to
more accurate eruption forecasts in the future.
Pyroclastic Flows
and Lahars
In the same way that the gases in a can of soda
cause the liquid to explode when shaken and
opened, the gases exploding out of the viscous
magma can cause pyroclastic fows to blast down
the fanks of the volcano at speeds exceeding
100 miles per hour when either a plume or
overstepped dome collapses. Pyroclastic fows
are hot, dry, gaseous avalanches that incorporate
lava fragments ranging in size from as large as
boulders to as small as ash. With temperatures of
up to 1500ºF, pyroclastic fows rapidly melt the
glacial ice and snow that cap these volcanoes,
creating rivers of mud known as lahars. Some
lahars begin fowing long after the volcano
erupts when rain is absorbed by the pyroclastic
material. Both lahars and pyroclastic fows
can travel for miles and can bury or destroy
everything in their path.
Adapted from wikimedia public domain
“One learns that the world, though made, is yet
being made.” ~ John Muir
Although Iliamna regularly emits plumes of
steam, it has not had a confrmed eruption in
recorded history. Redoubt, however, has erupted
at least 30 times in the last 10,000 years, and four
eruptive events have been confrmed in the last
century alone.
1902
Multiple between January and June
1966-68: 11 explosions (6 in ‘66 & 5 in ‘68)
1989-90: 23 “major explosive events”
2009
19 “major ash producing explosions”
April 1990 eruption courtesy of R.J. Clucas/ USGS
A Living Land
Image courtesy of Alaska DGGS
Redoubt and Iliamna do not stand alone. They
are but two of 52 historically active volcanoes
that rise above the Alaska-Aleutian subduction
zone, including nearby Spurr and Augustine.
This, in turn, is part of the “Ring of Fire,”
a zone encircling the Pacifc Ocean where
various oceanic plates are subducting beneath
continental plates. This area is home to the
majority of the world’s great earthquakes and
active volcanoes.
Pyroclastic fow courtesy of AVO/USGS
Ring of Fire
Volcanic Ash
Drift River lahar courtesy of NASA
Redoubt’s 2009 cycle of eruptions produced
at least fve pyroclastic fows and 20 lahars.
The largest lahar occurred on April 4th, 2009.
Consisting primarily of sand, andesite, and
water, it fowed 20.5 miles down the Drift River
to Cook Inlet, and was up to 2 miles wide and 19
feet deep in some places.
Volcanic ash can pose a myriad of hazards. For example, imagine this - you are aboard a Boeing
747 jumbo jet on December 15, 1989 when it fies into a difuse ash cloud erupted from Redoubt
Volcano. One by one you hear the engines stop running as silica-rich ash is ingested into the
engines and melts into a glassy coating that clogs the turbines and prevents them from spinning.
For the next eight minutes the jet descends 18,000 feet out of the sky. No doubt the longest eight
minutes of your life. With only 6,000 feet and three minutes remaining before the plane crashes
into the mountainous terrain below, the coating chills and cracks allowing the pilots to restart the
engines. Fortunately, nobody was injured; however, the cost to repair the plane was $80 million.
In order to prevent another potentially deadly accident, more than 385 fights afecting more than
20,000 passengers were either canceled, rerouted, diverted or turned back during Redoubt’s 2009
eruption.
E X P E R I E N C E Y O U R A M E R I C A™
Updated September 2015