Two Volcanoes Erupting in Alaska

Two Volcanoes Erupting in Alaska
Scientists are monitoring and providing alerts on Pavlof and Cleveland volcanoes
by Jessica Robertson
United States Geological Survey





Two of Alaska’s most active volcanoes—Pavlof and Cleveland—are currently erupting. At the time of this post, their activity continues at low levels, but energetic explosions could occur without warning.

Located close to the western end of the Alaska Peninsula, Pavlof is one of the most active volcanoes in the Aleutian arc, having erupted more than 40 times since the late 1700’s.

Pavlof has been erupting since May 13, 2013, with relatively low-energy lava fountaining and minor emissions of ash, steam, and gas. So far, volcanic ash from this eruption has reached as high as 22,000 feet above sea level. The ash plume has interfered with regional airlines and resulted in trace amounts of ash fall on nearby communities. The ash plume is currently too low to impact commercial airliners that fly between North America and Asia at altitudes generally above 30,000 feet.

Cleveland, located on Chuginadak Island in the Aleutian Islands, is also one of Alaska’s most persistently active volcanoes. It has exhibited some sign of unrest almost annually since the early 1980’s, with at least 19 confirmed eruptive events since then.

The current episode of eruptive activity at Cleveland has been characterized by single, discrete explosions, minor ash emissions, and small flows of lava and debris on the upper flanks of the volcano. On several occasions, ash-producing explosions have occurred reaching as high as 35,000 feet.

A small lava dome formed in the summit crater of Cleveland volcano in late January, 2013. At that time, the dome was about 300 feet in diameter and remained that size until a brief eruption on May 4 explosively removed a portion of the dome. The presence of a lava dome increases the possibility of an explosive eruption, but it does not necessarily indicate that one will occur.

Start with Science

The U.S. Geological Survey (USGS) is responsible for monitoring and issuing timely warnings of potential volcano activity. The USGS and its partners operate five volcano observatories, and monitoring of these two volcanoes is coordinated through the Alaska Volcano Observatory (AVO).

AVO is a joint program of the USGS, University of Alaska Fairbanks Geophysical Institute, and the State of Alaska Division of Geological and Geophysical Surveys.

Scientists at AVO were able to detect unrest at both Pavlof and Cleveland volcanoes that confirmed eruptive activity was occurring. AVO immediately sent notifications out to emergency-management authorities and those potentially affected.

When Will the Eruptions Stop?

Volcanic eruptions can last weeks to months, and sometime years, so the exact timing is unknown for when these two volcanoes will rest. AVO will continue to monitor them and provide updates in the event of future activity.

Detecting Signs of Unrest

Signs that the volcanoes were becoming restless were determined through a combination of monitoring data.

At Pavlof, a strong thermal signal was observed in satellite data at the summit that coincided with elevated seismic levels. Soon after these observations were made, more satellite data and pilot reports indicated that ash emissions were occurring.

At Cleveland volcano, explosions from the summit vent were detected by an infrasound array and seismic instruments on Umnak Island about 80 miles to the east, and later a thermal feature was observed at the summit in satellite imagery, which indicated hot material at or near the surface. The pressure sensors in the infrasound array pick up air waves generated by volcanic explosions. Because of the relatively slow speed of these waves, it took nearly 40 minutes to detect the explosion from that distance and issue an alert.

Ash Cloud Forecasts

AVO’s analysis of the eruption, including the amount of ash and the duration of the explosive phases, are key inputs into the forecasts by National Oceanic and Atmospheric Administration’s National Weather Service (NWS) of where the ash cloud will form and drift. These forecasts by NWS are used by the aviation industry to avoid flying into the ash.

The USGS developed a new ash cloud dispersal and fallout tool—a computer model known as Ash3d—that is being employed by AVO. The tool details where, when, and the amount of ash fall that is expected to occur. This information helps guide decisions on whether planes can safely land or depart, health warnings, potential impacts to infrastructure, and even when ash will stop falling and cleanup can begin.

Monitoring Tools

Pavlof is monitored with on-the-ground seismic stations (although only three of the seven instruments are currently operational), satellite remote sensing, and web cameras operated by the Federal Aviation Administration (FAA). A regional infrasound network operated by the University of Alaska Geophysical Institute has also helped detect explosions from Pavlof and Cleveland volcanoes.

Cleveland does not have a local seismic network and is monitored using only distant seismic and infrasound instruments and satellite data. Without local seismic instrumentation, scientists cannot forecast eruptions and smaller eruptions can be missed, especially because in the Aleutians, clouds commonly obscure the volcanoes in satellite data.

Updated Alerts and Webcams

Visit the AVO website for updated alerts and activity reports on Pavlof and Cleveland volcanoes. Virtually travel to these locations through an AVO webcam of Cleveland volcano and a FAA webcam located in Cold Bay about 37 miles west of Pavlof.

Alaska has 31% of all Active Volcanoes in the United States

Alaska’s volcanoes make up about 31% of all active volcanoes in the United States. There are 52 that have been active within the last 10,000 years and can be expected to erupt again. At present, 28 are monitored with ground-based instrumentation, and all are monitored daily using satellite remote sensing.

See a full list of all volcanoes in Alaska and view an interactive map of their location.

Although most of the volcanoes in Alaska are remote and not close to populated areas, millions of dollars of air freight and 20,000-30,000 people fly over active Alaskan volcanoes daily traveling between North America and Asia. In fact, the Anchorage International Airport is ranked the fifth busiest air cargo hub in the world based on tonnage. In addition to the threat that volcanic ash poses for aviation safety, the economic impacts due to disruption of air traffic can be substantial. One study estimated costs of five billion dollars from the week-long closure of European airspace caused by the eruption of Iceland’s Eyjafjallajökull volcano in 2010.

USGS Science for Volcano Hazards

USGS science is helping keep what are natural events from turning into major disasters.

The United States has approximately 169 active volcanoes, and more than half of them could erupt explosively. When the violent energy of a volcano is unleashed, the results can be catastrophic. Lava flows, debris avalanches, and explosive blasts have devastated communities. Noxious volcanic gas emissions have caused widespread lung problems. Airborne ash clouds from explosive eruptions have caused millions of dollars damage, including causing engines to shut down in flight.

To keep communities safe, it is essential to monitor volcanoes so that the public knows when unrest begins and what hazards can be expected. USGS efforts have improved global understanding of how volcanoes work and how to live safely with volcanic eruptions.

The USGS Volcano Hazards Program operates a total of five volcano observatories in cooperation with universities and state agencies. They are the Cascades Volcano Observatory, Yellowstone Volcano Observatory, California Volcano Observatory, Hawaiian Volcano Observatory, and Alaska Volcano Observatory. USGS also monitors and reports on volcanoes in the northern Marianas Islands.

In April, 2013, AVO celebrated 25 years of monitoring and studying Alaska volcanoes.

Learn More

Find out about the National Volcano Early Warning System (NVEWS), which is a proposed national-scale plan to ensure that volcanoes are monitored at appropriate levels given their associated threats.

Watch a video about USGS science on volcano hazards.

Major Earthquakes in Russia and the Sierra Nevada: 22-28 May 2013

The week of 22-28 May 2013 was punctuated by some big earthquakes – including the largest of the year to date, a magnitude M8.3 (M8.3) which occurred in the Sea of Okhotsk in the north west Pacific Ocean and was followed by an aftershock of M6.8.

There was also a tremor of M7.4 in Tonga which, in any other week, would have been comfortably in the running for the week’s largest seismic event.
These earthquakes and their aftershocks contributed to a total of over 1500 recorded tremors on the United States Geological Survey’s real time earthquake map (which includes all magnitudes recorded in the US and those of at least M4.0 elsewhere in the world). Of these, 33 were of at least M5.0.

The distribution of the larger shocks, as usual, tended to concentrate on the planet’s destructive plate boundaries, where subduction occurs, but the compressional zone of southern Eurasia also saw several tremors.

The Week’s Largest Earthquake: M8.3, Sea of Okhotsk

The dominant seismic event was the M8.3 which struck in the Sea of Okhotsk, to the west of Russia’s Kamchatka Peninsula. It isn’t clear whether this tremor is directly associated with the on-going swarm of smaller earthquakes which occurred on the Pacific side of the peninsular. Although both are associated with the subduction of the westward-moving Pacific plate below the Okhotsk microplate, the locations are hundreds of miles apart.

The Sea of Okhotsk earthquake, along with its M6.8 aftershock, is notable for its extreme depth. Typically, subducting ocean crust is heated as it descends and becomes softer, reducing the chance of major rupturing at depth. The reason may be related to the fact that in this area, some of the oldest ocean crust is found and old crust is generally colder and more rigid and thus more likely to rupture rather than deform. The USGS records show that other large deep earthquakes have taken place in this location. Despite their size, however, such deep earthquakes are less likely to cause damage than those closer to the surface

Mediterranean Earthquakes: Legacy of a Past Ocean

The southern margin of Europe was the focus for three earthquakes of above M4.5 this week, in Greece, Crete and Algeria.

Though none of these was of significant magnitude, they are interesting because all are part of the confused tectonic setting of the Mediterranean Sea, with a broad subduction setting confused by a complication of minor plates and crustal slices, subduction and lateral strike slip zones.

As continents move, oceans open and close: the Tethys Ocean lay between the former continents of Laurasia and Gondwana for millions of years until the reconfiguration of the continents, and the closing of Africa, India and Arabia with Eurasia narrowed and finally closed the ocean.

The Mediterranean is one of the few remaining basins of the former Tethys and, as such, represents the last stage of ocean evolution.

Earthquakes in the US: Sierra Nevada

US earthquake activity was dominated by the M5.7 tremor which occurred in the Sierra Nevada. With its epicentre near Lake Almayor, in Mount Lassen Volcanic Park, California, the tremor and its aftershocks (286 recorded to date) not only provided a focus for many tremors but also comfortably produced the four largest earthquakes of the week in the lower 48 states.

Large earthquakes are not uncommon in the western US, where extensional tectonics leads to regular and repeated normal faulting (one block slipping down relative to its neighbour) which dominates the scenery. This week’s tremor was relatively unusual, however, in that it occurred within the usually stable Sierra Nevada, rather than at its edge.

This Week’s Quakes: Usual or Unusual?

As well as producing a high number of larger tremors, the week threw up two particularly interesting anomalies. Both the Sierra Nevada and the Sea of Okhotsk earthquakes were ‘normal’ in terms of the magnitude for their general setting (the western Pacific and Western US respectively). Each, however, proved to be relatively unusual, the one in terms of its precise location and the other in terms of its depth.

Sources

USGS. M8.3 – Sea of Okhotsk. Accessed 28 May 2013
USGS. Real time earthquake map. Accessed 28 May 2013

So, last week there were a few earthquakes, now there's a volcano in Chile, and a few volcanoes in Alaska. We starting to get into a bit of a geologically active period, do you think, with one event helping trigger the next? Didn't something similar happen back in 2010, where there were a few large earthquakes (Haiti, Chile) in quick succession?

Earthquakes in the US: Sierra Nevada

US earthquake activity was dominated by the M5.7 tremor which occurred in the Sierra Nevada. With its epicentre near Lake Almayor, in Mount Lassen Volcanic Park, California, the tremor and its aftershocks (286 recorded to date) not only provided a focus for many tremors but also comfortably produced the four largest earthquakes of the week in the lower 48 states.

Large earthquakes are not uncommon in the western US, where extensional tectonics leads to regular and repeated normal faulting (one block slipping down relative to its neighbour) which dominates the scenery. This week’s tremor was relatively unusual, however, in that it occurred within the usually stable Sierra Nevada, rather than at its edge.

Lake Almanor, not Almayor, is located just south of Lassen Volcanic National Park in the extreme north-east Sierra Nevada (Mt Lassen marks the southern end of the Cascades range, where the Sierra Nevada transitions into an active volcanic arc). This are is bisected by many known Holocene faults.

Many geologists active in the Feather River drainage and neighboring areas of the northern Sierra Nevada have noted ample evidence of active tectonics and orogenic uplift. I think the notion of a stable Sierran Microplate is faulty, as the northern Sierra Nevada, southern Sierra Nevada, and Southern San Joaquin Valley are currently undergoing uplift and faulting. The extent of active deformation in the central Sierra Nevada isn't completely understood, but from the existing work appears to be minimal.

So, last week there were a few earthquakes, now there's a volcano in Chile, and a few volcanoes in Alaska. We starting to get into a bit of a geologically active period, do you think, with one event helping trigger the next? Didn't something similar happen back in 2010, where there were a few large earthquakes (Haiti, Chile) in quick succession?

I don't think there is any scientifically defensible reason to correlate these events. So far as I can tell, its all entirely coincidental.

Bryant wrote:
I don't think there is any scientifically defensible reason to correlate these events. So far as I can tell, its all entirely coincidental.

So I haven't come up with a revolutionary new theory then? Ah well, back to the day job.....