AVO can no longer seismically monitor the following volcanoes because of seismic station outages. As a result, AVO is unable to (1) assess whether these volcanoes may be building towards an eruption and (2) quickly confirm or dismiss reports of activity at these volcanoes.
Veniaminof
Aniakchak
Fourpeaked
Korovin
Because these volcanoes are no longer seismically monitored, they will move from volcano alert level Normal and aviation color code Green to "unassigned". They will likely remain without real-time seismic monitoring until next summer, when necessary upgrades at these and other networks will occur. As at other volcanoes without real-time seismic networks, AVO will continue to use satellite data and reports from pilots and ground observers to detect signs of eruptive activity.
On Wednesday, June 6, AVO lowered the Aviation Color Code at Fourpeaked from yellow to GREEN, and the Volcanic Activity Alert Level from advisory to NORMAL, on the basis of declining rates of seismicity and gas emission. At this time, AVO sees no indication that a sudden eruption of Fourpeaked is likely. Local hazards still exist near the summit, including jetting steam and/or very small explosions, unstable snow and ice, hot water and rock, and the possibility for high concentrations of dangerous volcanic gas.
AVO is lowering the Aviation Color Code for Fourpeaked Volcano from YELLOW to GREEN and the Volcanic Activity Alert Level from ADVISORY to NORMAL based on declining rates of seismicity and gas emission. At this time, AVO sees no indication that a sudden eruption of Fourpeaked is likely. Local hazards still exist near the summit, including jetting steam and/or very small explosions, unstable snow and ice, hot water and rock, and the possibility for high concentrations of dangerous volcanic gas.
Following the initial unrest at Fourpeaked, AVO installed a telemetered, geophysical monitoring network, consisting of three short-period seismometers, two co-located pressure sensors, and a web camera. These new instruments augment a pre-existing regional network that includes two seismometers within 60 km of Fourpeaked. The network operated successfully through the winter, and continues to record seismic activity; AVO has located nearly 400 earthquakes since installing the Fourpeaked seismic network. Most of these events occurred between November 2006 and February 2007. AVO located 33 earthquakes in March 2007, 20 in April, and 7 in May.
AVO has flown 7 gas monitoring flights since September 2006. Initial measurements showed high rates (1000s of tons/day) of SO2 emission. Subsequent flights showed declining emission rates, with the most recent measurement, taken in mid-May 2007, yeilding only about 50 tons/day of SO2.
In late September 2006, AVO presented a short list of scenarios describing possible future eruptive activity at Fourpeaked. At that time, AVO ranked a small to moderate eruption as the most likely scenario, with the possibility of no eruption occurring being only slightly less probable. A large eruption was not ruled out, but was considered much less likely than the other two scenarios. Based on the declining rates of seismicity and gas emission, and on the eight months that have elapsed without eruptive activity, AVO now considers the most likely scenario to be a gradual return to quiescence. If the current trend at Fourpeaked reverses toward an increasing likelihood of eruption, geophysical instrumentation would likely detect marked precursory activity.
Seismic activity at Fourpeaked remains elevated. On May 18, USGS scientists made airborne gas measurements at Fourpeaked and found that gas emissions have declined from the values last measured in February. This may mean that the present period of unrest is coming to an end, or that the hydrothermal system has become modified and is inhibiting gas emission. Visual observations of the volcano were limited this week as clouds and fog obscured views of the volcano by satellite and web camera.
Seismic activity at Fourpeaked remains elevated. Satellite and web camera views were cloudy through most of the week. A few clear webcam images showed the usual steam plume from the volcano's summit.
AVO is adding Fourpeaked Volcano to its list of seismically monitored Alaskan volcanoes. On September 17, 2006 two steam plumes were observed rising from Fourpeaked to an altitude of about 6,000 m above sea level (20,000 feet). Subsequent gas measurements showed a significant amount of SO2 coming from the volcano. Following these events, AVO installed a monitoring network on Fourpeaked, consisting of three new short-period seismometers, two co-located pressure sensors, one pre-existing short-period seismometer at Cape Douglas, and a web camera. The network has operated successfully through the winter and has recorded 380 locatable earthquakes. Pressure sensors have recorded pressure transients that may represent small explosions near the volcano's summit. The addition of Fourpeaked Volcano brings the total of seismically monitored volcanoes to 31.
Intermittent seismic activity continued at Fourpeaked. Satellite and web camera views were cloudy through most of the week. Clear weather late in the day on April 26th and on the 27th revealed nothing unusual in web camera or satellite views of the volcano.
Intermittent seismic activity continues at Fourpeaked. Satellite and webcam views were cloudy through most of the week, though clear weather on April 17th revealed nothing unusual.
Intermittent seismic activity continues at Fourpeaked. Very small explosion signals continue to be recorded intermittently by the AVO sensor network. Nothing unusual was noted in clear satellite and webcam views during much of the week.
Intermittent seismic activity continues at Fourpeaked. Clouds obscured views of the volcano by satellite and web camera for much of the week. Nothing unusual was noted in clear views.
Intermittent seismic activity continues at Fourpeaked. Several very small explosions were detected during the week. These events cannot be correlated with surface activity and do not indicate a significant change at the volcano. Clear web camara images during the week showed a decreased level of steam emission from vents near the summit.
Elevated seismicity continues at Fourpeaked volcano. A seismometer and pressure sensor located near the summit recorded occasional small explosions throughout the week. These events could not be correlated with distinct steam emissions and do not indicate a significant change in the character of activity at Fourpeaked volcano. Web camera images throughout the week show continued steaming at the summit. Clear views of the volcano by satellite showed no unusual activity.
Elevated seismicity continues at Fourpeaked volcano and occasional small explosions were recorded by a seismometer and pressure sensor located near the summit. These events could not be correlated with distinct steam emissions and do not indicate a significant change in the character of activity at Fourpeaked volcano. Web camera images throughout the week show continued steaming at the summit. Clear views of the volcano by satellite showed no unusual activity.
Elevated seismicity continues at Fourpeaked volcano and occasional small explosions were recorded by the pressure sensor located near the summit. These events could not be correlated with distinct steam emissions and do not indicate a significant change in the character of activity at Fourpeaked volcano. Web camera images throughout the week show continued steaming at the summit. Intermittent clear views of the volcano by satellite showed no unusual activity.
Elevated seismicity continues at Fourpeaked volcano. Web camera images show continued steaming at the summit. Intermittent clear views of the volcano by satellite showed no unusual activity this week.
Elevated seismicity continues at Fourpeaked. On February 18 Fourpeaked had a small swarm of 13 locatable earthquakes. The largest was a M1.8. A gas flight on February 23 recorded continued output of SO2. Webcam images show continued steaming at Fourpeaked's summit. Nothing unusual was observed in satelite views.
Low-level seismic unrest continues at Fourpeaked volcano. Small explosions continue to be recorded by seismic and acoustic instruments. Occasional clear webcam images showed steaming from the summit vents.
Low-level seismic unrest continues at Fourpeaked volcano. Three small explosive events were recorded by seismic and acoustic instruments Thursday and Friday (February 08-09) beginning at 10:36 AM AKST (1936 UTC) February 08. A possible large steam plume was observed in several partly cloudy satellite views Thursday afternoon. Low clouds obscured the webcam views of the summit. Earlier this week, webcam images showed steaming from the summit vents.
Low-level seismic unrest continues at Fourpeaked volcano. Cloudy conditions have obscured views of the volcano by satellite this past week. A brief clear view on Thursday showed continued gas emission at the summit.
Low-level seismic unrest continues at Fourpeaked volcano. Clear views of the volcano in web camera images showed continued steaming from the summit area. AVO is planning an airborne gas survey and observation flight to the volcano as soon as weather allows.
Low-level seismic unrest continues at Fourpeaked volcano. No unusual changes in seisimic activity have occurred over the past week, and the volcano has been obscured by clouds most of the week. Clear views of the volcano in web camera images this morning show only minor steaming from the ice encircled fumaroles near the summit. Cloud cover prevented observations of the volcano by satellite throughout the week. AVO has received no new information from passing aviators about unrest or volcanic emissions at Fourpeaked volcano this week.
Low-level earthquake and fumarolic activity continue at Fourpeaked volcano. A slight increase in seisimic activity has been observed in the past two days but is not considered unusual. Typical steam and gas emissions from vents near the summit were observed in clear web camera images this week. Nothing unusual was seen in clear satellite images early this week. Cloudy conditions have obscured views of the volcano by satellite and web camera since Wednesday of this week.
Low-level earthquake and fumarolic activity continue at Fourpeaked volcano. Typical steam and gas emissions from vents near the summit were observed in web camera images during clear weather this week. Nothing unusual was seen in satellite images.
Low-level earthquake and fumarolic activity continue at Fourpeaked volcano. Typical steam and gas emissions from vents near the summit were observed in web camera images during clear weather this week. Nothing unusual was seen in satellite images.
Low-level earthquake activity continued this week at Fourpeaked volcano. Several clear satellite views this week showed nothing unusual. Clear webcam views showed continued steaming from the summit.
Low-level earthquake activity continued this week at Fourpeaked volcano. Nothing unusual was detected in variably cloudy satellite views. Both today and Wednesday, however, clear weather revealed continued steaming at the summit, visible in web camera images.
Low-level earthquake activity and fumarolic activity continues at Fourpeaked volcano. Although clouds obscured the volcano in satellite and webcam images during most of the week, the web camera images early this morning showed continued fumarolic emissions.
Vigorous fumarolic and low-level earthquake activity continue at Fourpeaked volcano. The AVO web camera during the week showed a persistent steam and volcanic gas plume rising at most a few thousand feet (several hundred meters) above the summit. The most recent airborne gas survey on November 18 showed no significant change from previous measurements.
Low-level earthquake activity continues at Fourpeaked volcano. Web camera images this past week showed a persistent steam plume rising a few thousand feet (several hundred meters) above the summit. Nothing unusual was observed in clear satellite views obtained several times this week.
Low-level earthquake activity continues at Fourpeaked volcano. Web camera images this past week showed a persistent steam plume rising a few thousand feet (several hundred meters) above the summit. Nothing unusual was observed in clear satellite views obtained several times this week.
Low-level earthquake activity continues at Fourpeaked volcano. Web camera views this past week show a typical steam plume rising several hundred meters above the summit. Nothing unusual was observed in clear satellite views.
Low-level earthquake activity continues at Fourpeaked volcano. Web camera views this past week show a typical steam plume rising several hundred meters above the summit. Nothing unusual was observed in clear satellite views.
Gas measurements made on Monday indicate continued emission of sulfur dioxide from Fourpeaked Volcano. No earthquakes were located at Fourpeaked this week, and small, unlocated seismicity appears to have diminished. Visual observations from Monday's overflight show continued vigorous steaming and disruption of the summit glacier.
Earthquake activity and anomalous gas emissions continue at Fourpeaked. Favorable weather conditions this week allowed two field crews to conduct geologic investigation, and to install seismic equipment and a web camera at the volcano. The web camera is located 16 km (10 miles) north of Fourpeaked and views can be accessed on the AVO public website. Web camera views much of this week, showed a steam and gas plume rising from the craters near the summit of Fourpeaked volcano.
Earthquake activity and anomalous gas emissions continue at Fourpeaked. Although the volcano was cloud covered for most of the week, yesterday AVO observers were provided a glimpse of the two prominent vents, which continue to emit steam and gas profusely.
Volcanic unrest continues at Fourpeaked volcano. A seismometer installed on September 25 indicates that low-level seismicity at Fourpeaked has been ongoing throughout the week. Because we have only one station close enough to the volcano to detect most of these earthquakes, we are unable to locate them. An earthquake swarm on October 3 contained tens to hundreds of very small earthquakes.
Airborne gas measurements made on September 30 showed that high emission rates of sulfur dioxide continue at levels similar to those measured during the previous week. Poor weather has prevented any further field work.
Observations suggest the presence of new magma at shallow levels beneath the volcano. It remains possible that a significant eruption could occur in the coming days to months.
As weather allows, AVO will obtain further airborne gas measurements, install additional instrumentation, retrieve time-lapse images, and conduct further geologic investigations near the volcano.
Fourpeaked volcano is not known to have erupted historically and the age of the last eruption is not known. Geological investigations have been limited and ice covers much of the area. Because of this, the range of sizes and styles of past eruptions are not well-constrained. However, the composition of the volcano indicates that eruptions of Fourpeaked can be explosive, possibly producing plumes that reach in excess of 10 km (33,000 ft) above sea level and local ashfall.
Volcanic unrest continues at Fourpeaked volcano. Despite poor weather since our last visit to the volcano on Monday, satellite observations by scientists from the University of Maryland-Baltimore County indicate that sulfur dioxide emission is continuing.
Early in the week, AVO conducted several helicopter and fixed-wing missions to Fourpeaked. Observers photographed a linear series of vents running north from the summit for about 1 km (0.6 mi). Some of the vents were vigorously emitting steam and other volcanic gasses. Thermal measurements of up to 75 degrees C (167 degrees F) were recorded at the vents, although steam was likely obscuring hotter areas.
Adjacent glacial ice had been disrupted and showed signs of subsidence. Airborne gas measurements documented high emission rates of sulfur dioxide, hydrogren sulfide, and carbon dioxide, and a distinct sulfur smell was evident up to 50 km (30 mi) from Fourpeaked's summit. Deep scouring of a glacier flowing west from the summit indicated flooding, probably from the September 17th event.
Together, these observations strongly suggest the presence of new magma at shallow levels beneath the volcano. It remains possible that a significant eruption could occur in the coming days or weeks.
In addition to making observations this week, AVO staff have installed several seismic stations and a time-lapse camera and sampled ash and debris flow deposits from the September 17 event. Seismic data retrieved thus far indicates very low rates of volcanic earthquakes.
As weather allows, AVO will obtain further airborne gas measurements, install additional instrumentation, retrieve time-lapse images, and conduct further geologic investigations near the volcano.
On September 17, an explosion of ash, gas, and steam from Fourpeaked Mountain 320 km (200 mi) SW of Anchorage on the Alaska Peninsula marked the onset of unrest at this long-dormant, ice-clad volcano. AVO elevated the level of concern color code to YELLOW on September 20. Since then, AVO has gathered aerial and ground-based information and also initiated installation of geophysical instrumentation to better track activity at Fourpeaked. Based on our observations and limited geologic understanding of the volcano, it is possible that significant eruptive activity could occur in the coming days to weeks.
Over the weekend and continuing today, AVO flew a variety of missions to Fourpeaked volcano. The main findings are as follows: (1) Observers saw a linear series of vents running north from the summit for about 1 km (0.6 mi). Most of these vents were vigorously emitting steam and other volcanic gasses. In the immediate vicinity of the vents, the glacier had been disrupted and showed signs of subsidence. (2) Gas measurements reveal that emission rates of sulfur dioxide, hydrogren sulfide, and carbon dioxide were all high. The sulfur dioxide emission rate was roughly equivalent to that measured at Augustine before its January 2006 eruptions. A distinct sulfur smell was evident up to 50 km (30 mi) from Fourpeaked's summit. (3) Marked scouring of a glacier flowing west from the summit indicates flooding, probably from the September 17th event. (4) Thermal measurements of 60 degrees C (140 degrees F) where recorded at the vents, though the abundant steam was likely obscuring hotter areas.
All evidence, including the ash emission of September 17th, the abundant volcanic gases, the presence of new vents at the summit, and the disruption and floods occurring at and below the summit glaciers, suggest the presence of new magma at shallow levels beneath the volcano. Because AVO has had no instrumentation network on Fourpeaked, we do not have the geophysical measurements necessary to provide independent evidence for the presence of new magma.
Fourpeaked volcano is not known to have erupted in the last 10,000 years, though geological investigations have been limited and ice covers much of the area. Because of this, the range of sizes and styles of past eruptions is not well-constrained. However, the composition of the volcano indicates that eruptions of Fourpeaked can be explosive, possibly producing plumes that reach in excess of 10 km (33,000 ft) above sea level and local ashfall.
Based on all currently available evidence, AVO believes that an eruption from Fourpeaked in the next days to weeks is possible. Given below are some possible future scenarios for the current unrest at Fourpeaked, listed in order, with the most likely scenario listed first:
(1) A small to moderate eruption will occur, which may produce ash plumes exceeding 10 km (33,000 ft) above sea level. Lava flows may also occur.
(2) No eruption occurs. Unrest gradually subsides to background levels.
(3) A large eruption will occur, which would produce ash plumes exceeding 10 km (33,000 ft) above sea level, and possible widespread ash fall.
Even minor volcanic activity can result in floods, debris flows, and lahars (volcanic mud flows) into the nearby drainages. These can occur without obvious signs of volcanic activity like ash plumes or loud explosions. Thus the local area is considered especially hazardous.
AVO has begun constructing a network of geophysical monitoring instruments at Fourpeaked. Over the last two days, two seismometers were installed between 10 and 20 km (6 – 12 mi) from the summit. These instruments give AVO volcanic earthquake detection capability, but do not provide enough information for short-term forecasts of volcanic eruptions. Additional seismometers will be installed in the coming days. If conditions permit, these instruments will be closer to the summit and should provide better forecasting capability. AVO also plans the installation of web cameras and instruments for measuring ground deformation.
AVO will continue to monitor the volcano with satellite data, observation flights, and new geophysical data streams as they become available.
AVO raised the Level of Concern Color Code for Fourpeaked volcano from “Not Assigned” to YELLOW on Wednesday, September 20. A large steam explosion near the summit of Fourpeaked volcano occurred on Sunday, September 17 beginning at approximately 12:00 noon AKDT (2000 UTC, September 18). Photographs and NEXRAD weather radar show that the plume reached up to approximately 20,000 ft (6,000 m) above sea level. Satellite images showed a cloud originating from Fourpeaked volcano, and persisting throughout the night. No ash or thermal anomalies have been detected in satellite images. The plume was visible on NEXRAD until 9:45 PM AKDT September 17 (0545 September 18 UTC). AVO staff conducted both fixed-wing and helicopter overflights in the Cape Douglas area September 20 and confirmed the source of volcanic activity to be Fourpeaked volcano.
A small but distinct SO2 cloud over the area was detected by researchers from the Univ. of Maryland-Baltimore County using a new NASA satellite-based UV sensor (the Ozone Mapping Instrument, or OMI) at 3:00 PM AKDT (2300 UTC) September 17. Puff windfield modeling showed that the plume would have spread west and then moved north over the next day or so. This is consistent with pilot reports received by AVO on September 18 that described a strong sulfur smell in the Stony River Valley, ~200 miles west of Anchorage. Subsequent passes of the OMI have also shown an SO2 cloud whose position is consistent with Puff modeling. AVO has received several accounts of very light ashfall, in Homer and near Nonvianuk Lake in Katmai National Park, that are also consistent with Puff modeling.
There is currently no real-time local seismic network on the volcano. The closest seismometer is 40 miles (64 km) to the north. A small swarm of tectonic earthquakes was detected on the regional seismic network from 11:48 AM to 3:50 PM AKDT (19:48 to 23:50 UTC) September 17. No explosion signals were detected seismically, but the infrasound array at the University of Alaska-Fairbanks picked up a signal from the Fourpeaked area with an origin time consistent with the other data.
There have been no known historical eruptions of Fourpeaked and no known geologic evidence for activity in the last 10,000 years. These factors and the lack of close-in seismic monitoring limit AVO’s ability to forecast likely future activity. A helicopter flight is scheduled for this weekend to make geologic observations, collect samples, and install telemetered seismometers. AVO continues to monitor Fourpeaked using satellite images.
On Sunday evening, September 17, AVO received numerous reports of a large unusual cloud rising to heights of 20,000 ft (6,000 m) above sea level from the Cape Douglas area, about 200 miles (320 km) southwest of Anchorage and about 80 miles (140 km) northwest of Kodiak. Since our Monday, September 18 Information Release, additional data and observations of the September 17 event have been compiled from several new sources. These data confirm that the source of the large cloud observed Sunday evening was volcanic. Thus, AVO is increasing the Level of Concern Color Code for Fourpeaked volcano from “Not Assigned” to YELLOW
The exact location of the source is still unknown. Satellite and radar data suggest a source low on the flank of Fourpeaked volcano and we are assigning this activity to Fourpeaked based on this data. However, this location has not yet been confirmed by visual observations.
New details of Sunday’s event have been added since Monday afternoon:
Retrospective analysis of data from the NEXRAD Doppler radar in King Salmon show an unusual cloud starting at 12:00 PM AKDT (2000 UTC) on September 17. The maximum cloud height determined by radar during the first hour of the event was 20,000 ft (6,000 m). The radar return from the cloud continued until at least 9:45PM AKDT (0545 UTC).
A cloud of sulfur dioxide gas released during the eruption was observed by colleagues at the University of Maryland Baltimore County over Cape Douglas/Fourpeaked region on September 17, 2006 at 3:00PM AKDT (2300 UTC) using data collected by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite.
Puff particle dispersion modeling showed that the cloud would have spread west to east as it moved northwards over the subsequent day. This is consistent with pilot reports received by AVO on the afternoon of Monday, September 18, that described a strong sulfur smell in the Stony River Valley, 300 km (180 miles) northwest of the Fourpeaked area, and from additional OMI sulfur dioxide observations of the cloud.
Although satellite data did not detect ash during this event, AVO received reports of a trace of ashfall at Nonvianuk Lake outlet (110 km, about 70 miles, west-northwest of the volcano) and near Homer (about 95 miles northeast of the volcano).
Although poor weather in the area has prevented visual observations, NEXRAD data over the past two days have not detected any further emissions. AVO staff will attempt both fixed-winged and helicopter overflights this afternoon to locate the possible vent areas and document any changes. AVO continues to monitor satellite data for further signs of activity.
On Sunday, September 17, AVO received several reports of two discrete plumes rising from the Cape Douglas area, about 200 miles (320 km) southwest of Anchorage, beginning at approximately 8:15 PM AKDT (0415 UTC, September 18) and continuing until darkness. Analysis of satellite images shows that the plumes originated in the area of Fourpeaked Glacier, located between Fourpeaked and Douglas volcanoes. Photographs of the plumes show that they reached up to approximately 20,000 ft (6,000 m) above sea level.
Satellite images show a cloud originating from Fourpeaked glacier area and persisting throughout the night. The cloud does not show an ash signature. The cloud traveled up to 12 miles (20 km) to the northeast.
Fourpeaked and Douglas volcanoes are not monitored seismically. Seismometers around the Katmai group of volcanoes, about 50 miles (80 km) to the southwest, and around Augustine volcano, 40 miles (64 km) to the north, did not record any unusual seismic activity. Based on the absence of an ash signature in the cloud in satellite data, a significant volcanic eruption did not occur. The origin of the two plumes is still unknown.
Poor weather in the area today prevents further visual observations. AVO will continue to monitor the area via satellite and local pilot reports. AVO will attempt an overflight of the area later this week.
2009-11-17 11:32:46 - VAN/VONA
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