Mount Spurr is a Quaternary stratovolcano located near the northeastern
end of the Aleutian
volcanic arc. It is the easternmost historically active volcano in
the Aleutian arc and is the
highest of several snow- and ice-covered peaks that appear to define
a large, dissected stratovolcano.
Mount Spurr volcano, 3,374 m (11,070 ft) high, is visible on the skyline
125 km
(78 mi) west of Anchorage, Alaska.
As
shown here, prior to its 1992 eruptions, Crater Peak,
a satellite vent of Mount Spurr volcano, contained a warm lake about
100 m (330 ft) across.
Photograph
by D. Turner, University of Alaska Fairbanks , 1986.
The youngest volcanic feature at Mount Spurr is a satellitic cone,
Crater Peak, located in the
breach in the caldera about 3.2 km south of Mount Spurr. Crater Peak
has been the source
of all Late Holocene eruptive activity at Mt. Spurr. Before the 1992
eruption, a small crater
lake occupied the bottom of the crater.
Modified from USGS 1:250000 scale topographic geotiff
files. From AVO
Saturday, September 25th, 2004
AVO measured gasesbeing emitted by Crater Peak and Mount Spurr
during a fixed-wing flight
on September 15. The combined output of carbon dioxide (CO2) from
the two vents was
approximately 2300 tons/day, an increase from the approximately 760
tons/day measured
August 7-8. The gray color of the lake at the bottom of the ice cauldron
is typical of crater
lakes containing dissolved sulfurdioxide, or SO2. These observations
further suggest that
magma resides beneath the volcano.
September
19th, 2004
As per September 17th, AVO has issued the following report:
Elevated levels of seismicity continue to be recorded at Mt. Spurr
volcano.
Seismicity has not changed significantly from that observed in the
past few
weeks. This week, we located about 85 earthquakes within 30 km of
the
summit with an average of approximately 12 per day, similar to the
level of
last week. Although this rate of seismicity is greater than typical
background levels there are no indications that an eruption is imminent.
This type of seismic activity could diminish over time and is not
necessarily a precursor to an eruption. Observations of the summit
during
AVO overflights this week showed no major changes at the summit compared
to
last week.
From AVO's page: "What's going on at Mt. Spurr?":
An
eruption of Mount Spurr, if it occurs, will likely be preceded by
further changes in
activity. Earthquakes will likely increase both in number of events
and size. As magma
moves from beneath the volcano toward the surface, it will break surrounding
rock and
thereby trigger earthquakes along its path. Emissions of volcanic
gases are likely to
both increase in volume and change in content before an eruption begins.
When
magma rises into a volcano, it causes the earth’s crust to swell
in response. This
swelling is usually, but not always, very small, and is only detected
with very sensitive
GPS instruments. New instrumentation will monitor these changes.
After reading this, one just has to ask why the "melt
hole" on the summit of Mt. Spurr
has changed in shape if nothing happens?
Or, are those new pictures identic to the ones from the month before?
 
Left:
August 2nd, Right: September 7th-9th
Photo: Chris Waythomas and Sigrun Hreinsdottir
 
Left:
August 2nd, Right: September 7th-9th
Photo: Chris Waythomas and Sigrun Hreinsdottir
Are the last photos taken
from a closer distance, or is it just that I don't get the right picture???
From soneone* who knows better, we have received the
following comments today:
Yes, there is something different -- there is now a "pond"
in the crater of
Mt. Spurr and it has been changing slightly over a relatively short
period
of time. That is what you are seeing and why it looks a bit different
from
time-to-time.
*
SWVRC
Friday, August 13th, 2004
The National Weather Service reported early Thursday
that Mount Spurr had spewed a small
amount of ash, but later canceled its warning. And geologists who
study the volcano some
75 miles west of Anchorage say their sensors show no evidence of an
eruption.
"Someone thought they saw a plume (of ash), but
to our knowledge it was steam," they say
at the AVO. "There may have some steam activity that got people
excited, but to our
knowledge there has not been an eruption."
Observers from the volcano center flew to Mount Spurr by helicopter
and airplane
Thursday morning to check seismographic sensors on the flanks. The
sensors have detected
increasing activity in recent weeks, but nothing Thursday that suggested
ash had been ejected.
The weather service report was based on a call from a pilot at Hayes
River, some 50 miles
north of the mountain. The pilot reported early Thursday morning that
his airplane was covered
with a light coating of ash, which he thought was volcanic. The wind
was blowing in the right
direction, and forest fires in the eastern Interior were thought to
be too far away to drop ash
in the Susitna Valley. Then a satellite photo showed what might have
been an ash cloud.
Although an eruption couldn't be confirmed, the weather service issued
a "sigmet," or
significant meteorological event warning that the volcano had emitted
an ash cloud
"estimated by satellite to be about 20 (nautical miles) wide
and moving nnw."
"We're bound by international regulations to get them out,"
they said. "When we're sure it's not
(an eruption), we can cancel. But during that time you're not really
sure what's going on,
it's better to be safe than sorry."
Subsequent reports from pilots and satellite photos suggested no eruption
had occurred, and
the volcanic ash warnings were canceled around 10:15 a.m. But as late
as noon Thursday,
the agency's forecasts for areas n. and w. of Mount Spurr included
a "volcanic ash advisory."
Based on an article from Anchorage
Daily News
Notice
the increase in quakes before the 1992 eruption, which so far looks
similar to the increase we are observing now, and compare to the 2002
swarm.
After having done the investigations mentioned above, AVO issued the
following statement:
Based on these observations and our continuing seismic monitoring
of the volcano, there are
no signs that an eruption is imminent or even certain. Ephemeral summit
craters have been
described before at Mt. Spurr and temporary increases in earthquake
activity below a volcano
often decline without producing an eruption. AVO will continue to
monitor activity at
Mount Spurr closely using seismic data, satellite images, and overflights,
and will issue
further information releases as appropriate.
Saturday, August 7th, 2004
As of the 7th of August, the AVO, has reported
that elevated levels of seismicity continue
to be recorded at Mt. Spurr volcano and approximately 10-20 earthquakes
have been
recorded daily beneath the summit of Mt. Spurr. The collapse pit discovered
earlier this week
may indicate an increase in heat flux through the summit dome that
could be related to
the intrusion of magma at depth. During the week, AVO received photographs
of the
Mt. Spurr summit taken on June 20, 2004 that do not show a
collapse pit, but do indicate
the presence of an arc-shaped scarp in the area where the present
collapse pit has formed.
Wednesday, August 4th, 2004
A
minor depression has eveloped on Mt. Spurr August 2nd.
Photo: Chris Waythomas, USGS
As of the 4th of August, AVO has reported that an overflight of Mt.
Spurr by AVO
scientists yesterday afternoon revealed a circular depression in the
icecap just northeast of
the summit. The depression is approximately 50 meters in diameter
andabout 25 meters deep.
The floor of the depression contains an icy pond, with small areas
of open water.
No steam or volcanic emissions were observed. Depressions of this
sort may have existed
on Spurr before, but AVO is not aware of any in recent decades. The
depression may have
formed by heat from the volcano melting the ice, or, the release of
stored water, which might
account for the minor mudflows observed several weeks ago on the upper
flanks.
If due to heat, it is not known if the flow of heat to the surface
has increased and is related
to the recent increase in earthquake activity.
Crater Peak showed no sign of
any unusual activity. Earthquake activity continues beneath
Mt. Spurr with no significant change over the past week.
Wednesday, July 28th, 2004
Mount Spurr,
the volcano on Anchorage's doorstep, is kicking up once again, the
first time
since it erupted 12 years ago, scientists said this week.
Tiny
earthquakes by the hundreds have been rumbling beneath the mountain
across
Cook Inlet from the city, according to the Alaska Volcano Observatory
(AVO) in Anchorage.
The
observatory on Monday raised its official level of concern from Code
Green,
or "No eruption anticipated," to Yellow, meaning "An eruption is possible
in the next
few weeks and may occur with little or no additional warning."
The
mountain's recent activity began slowly in February and intensified
on July 4. An average
of 20 quakes are now occurring every day, a rate higher than at any
time since 1992.
The quakes are the only confirmed volcanic activity at Spurr
so far, indicative of the
movement deep below the mountain of magma, or molten rock and gases,
that is beginning to seek an outlet.
In
this sunset view (westward) from the rooftop of the Alaska Volcano Observatory
in Anchorage,
a prominent steam and gas plume rises from the Crater Peak vent, Mount
Spurr volcano.
Photograph by
M. Doukas, U.S. Geological Survey, October, 1992.
|
Three of the volcanoes closest to Anchorage recently blew their
stacks within a six-year
span, causing major problems. Besides Spurr,
Augustine Volcano in lower Cook Inlet
went off in March 1986, and Redoubt
Volcano across the Inlet from Kenai erupted
over several weeks in 1989 and 1990.
Shortly
after Redoubt's Dec. 15, 1989, eruption, a KLM jetliner flew into
the plume
as if it were a cloud bank, at about 28,000 feet over Talkeetna.
All four engines seized
up and shut off after sucking in the abrasive ash.
The
jetliner, carrying more than 230 people, fell silently from the
sky for more than two
miles. At 13,300 feet, the crew managed to restart the engines
and land safely at
Anchorage in a plane that had sustained $80 million in damage.
The
highest danger from volcanoes is to airplanes. Since 1980, at
least 14 other aircraft
flying along North Pacific air routes have been damaged because
crews unwittingly
flew through volcanic plumes, according to the Geological Survey.
From
www.avo.alaska.edu
See also our special page about aviation Click
here.
|
July 11th, 1953
The first historical eruption of Mt. Spurr occurred on July 9, 1953,
when the Crater Peak
vent, in two main eruptive pulses on two succeeding days, produced a
tephra blanket about
4 mm thick at Anchorage and detectable up to 350 km to the east. Ash
in the initial eruptive
pulse rose to 20 km. Lahars swept down valleys heading on the south
flank of Crater Peak,
resulting in a dam on the Chakachatna River, which raised the level
of Chakachamna Lake
at least 3 m. Activity was short-lived and essentially confined to the
two days.
A
plinian-type explosive eruption from the Crater Peak vent (hidden beneath
clouds) on Mt. Spurr, Alaska, sent an eruption column to a height of
about 18 km above sea level
Photograph by R. McGimsey,
USGS, on 18 August 1992
October 1st, 1992
The most recent eruption at the Mt. Spurr center began on June 27, 1992
with the first of
three explosive events that occurred over a three month period. A slow
but steady increase
in seismicity beneath and around the center began 10 months before the
eruption.
By early June, bursts of shallow tremor were occurring at Crater Peak
and the small crater
lake was showing dramatic changes including increased SO2/Cl ratios,
a change in color
from turquoise to gray, and vigorous upwelling.
An abrupt increase in tremor amplitude at 0705 on June 27 indicated
onset of the first
eruptive pulse. The volcano was hidden by clouds which prevented direct
observation.
During the 4 hour event, small pyroclastic flows mixed with snow swept
down the south flank
of the cone, and an ash plume rose to an estimated height of 14.5 km.
Close
aerial view, looking east, of the base of the vertical eruption column
from the
Crater Peak vent, Mount Spurr volcano.
Photograph by R. McGimsey,
U.S. Geological Survey, August 18, 1992.
The second eruptive phase of 1992 began on the afternoon
of August 18 preceded by
only a short tremor burst. C-band radar data indicates the ash plume
rose to about 14 km,
and small pyroclastic flows again descended the east and southeast flanks
of Crater Peak.
Anchorage International Airport was closed for 20 hours because of the
ashfall.
No precursory activity occurred until the late hours of September 16
when a 3-hour-long
increase in tremor culminated in an 11-minute-long eruptive event. An
hour and a half later,
a much larger eruptive phase began that lasted 3.5 hours. Pyroclastic
flows swept down
the south, east, and east-northeast flanks of Crater Peak . The flows
entrained snow and
other surface debris, developing into lahars, of which at least one
temporarily dammed the
Chakachatna River. Southwesterly winds carried the ash cloud across
upper Cook Inlet,
narrowly missing Anchorage, up the Matanuska Valley and across eastern
Alaska.
Space
Shuttle photo showing Mt. Spurr ejecta circling the globe
At least 1 mm of ash fell in Glenallen,
350 km east, and a very light dusting was reported at
Burwash Landing, Yukon Territory, 700 km east. Photographs taken from
the Space Shuttle
several days later show the thin but undispersed ash cloud over western
Quebec, Canada.
Bulk tephra volume was about 56 x 106 m3.
Search this site - Søk våre sider
|
