You are currently browsing the monthly archive for April 2009.

Updating the update: After further testing I’m now splitting the circle radius down the middle at 35 mi. I don’t know, I’ll probably change it again. The sensitivity seems to be about right based on cells that went through this morning. Email recipients can expect 1-3 emails depending on the sequence of cells moving through the zone. Inter-email time is set at 60 minutes, meaning once you get an email, you won’t get another for an hour, and not at all if conditions downgrade, so check the radar page if you have concerns about passing storms once you’ve been emailed. The timing is set in consideration of those who are not in the path of active weather when the emails hit.

Update: After extensive testing and calibration, I’m back to 40 mi radius. The sensitivity trip point has been raised to a 60 dBZ level.

Last night’s cold front passage was a trial by fire of sorts for EWR. If you were on the receiving end of a blizzard of alerts, I apologize for that. We are currently testing some very early new pre-releases of the next version of the program software, as well as fine-tuning the sensitivities of the system, and the combination is turning out to be a handful. Presently there are 3 computers running 4 versions of the software (no, not all at the same time!). Ephemerata Weather Radar currently uses two computers to generate the web updates when both scans are up. The goal eventually is to do that from one machine.

One thing I’ve done is to reduce the scan area from 40 mi. radius to a 30 mi. radius. With every new data update from the NWS, an alert is generated if conditions within the scan zone are met. Since it can take some time for a system to move through the zone, the potential exists for multiple alerts from the same storm pattern. The software has two different time loops to modulate the alert frequency and it will take some time to get these in sync. The target is for a maximum of 3 alerts over the course of a storm event moving through the zone.

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Solar ISN mean dips below 1.00

While the sun still struggles to form cycle 24 spots like seen in this weak plage area (upper right) in today’s SOHO MDI and Magnetograms (shown below) Paul Stanko of NOAA writes to tell me of an interesting development in his tracking of the International Sunspot Number (ISN).

shoho_mdi_042109


Paul writes:

My running mean of the International Sunspot Number for 2009 just dipped below 1.00. For anything comparable you now need to go back before 1913 (which scored a 1.43) which could mean we’re now competing directly with the Dalton Minimum.

Just in case you’d like another tidbit, here is something that puts our 20 to 30 day spotless runs in perspective… the mother of all spotless runs (in the heart of the Maunder Minimum, of course!) was from October 15, 1661 to August 2, 1671. It totaled 3579 consecutive spotless days, all of which had obs.

Errant counting of sunspecks from Catainia aside, it appears that we haven’t seen anything like this in modern history.

We live in interesting times.


For more about sunspot monitoring check out SOHO in the sidebar.

The Alaska Volcano Observatory has released a close-up photo of the building lava dome in Mt. Redoubt. There is on-going concern that the building dome may yet result in an explosive eruption. The more the dome builds, the more violent a subsequent eruption might be. Conversely, it could serve to seal the vent if there is insufficient pressure behind it.

This picture is a crop of the dome itself from the larger shot, and has been corrected for temperature at 6500K and contrast enhanced for definition. You can see what appears to be incandescent rock in the rubble pile, indicating that this is recent, still very hot rock.

Extract from the close-in view of the front of the active lava dome growing in the summit crater of Redoubt Volcano since April 4.  Picture Date: April 16, 2009 12:51:04 Image Creator: McGimsey, Game  Image courtesy of AVO/USGS.

Extract from the close-in view of the front of the active lava dome growing in the summit crater of Redoubt Volcano since April 4. Picture Date: April 16, 2009 12:51:04 Image Creator: McGimsey, Game Image courtesy of AVO/USGS.

A line of severe weather from a developing low crossed through Kentucky, Tennessee and on into Alabama, Arkansas, Georgia, South Carolina and northern Florida on Good Friday. Several tornados were spawned apparently, but the most damaging was a twister that dropped on the city of Murfreesboro (immediately south and slightly east of Nashville) in the early afternoon.

This video shows a animated series of scan images for the region starting from about 1:30 EDT. There are three scans – short range composite, storm relative velocity, and vertical integrated liquid. In particular, there is a signature in the vertical integrated liquid scan that looks like it may be that of the Murfreesboro tornado.

The following three VIL scan excerpts were taken at 1:53pm EDT, 1:57pm EDT and 2:07pm EDT. The arrows point to structures of interest.

Vertically Integrated Liquid, Nashville 17:53UTC (1:53 pm EDT), excerpt

Vertically Integrated Liquid, Nashville 17:53UTC (1:53 pm EDT), excerpt

Vertically Integrated Liquid, Nashville 17:57UTC (1:57 pm EDT), excerpt

Vertically Integrated Liquid, Nashville 17:57UTC (1:57 pm EDT), excerpt

In this second image, the arrows point to two interesting structures. The topmost may be the signature of the tornadic supercell that spawned the Murfreesboro tornado. There seems to have been a coalescence of the two cells evident in the first image. The circular form of high reflectivity is indicative of strong rotation in this cell, a “tube” of water, as it were.

The lower arrow points also to a interesting structure – this has maintained a very high reflectivity over several minutes, and in a tight configuration. I don’t have touchdown data yet to see if either of these structures were the cells that produced the tornado.

The third image, below, shows the same cells 10 minutes later, suggesting that some dissipation had occurred in the upper cells, whereas the lower one seems to be continuing to strengthen. I will leave off the warning boxes for greater clarity on future scan series.

Vertically Integrated Liquid, Nashville, 18:07UTC (2:07pm EDT), excerpt

Vertically Integrated Liquid, Nashville, 18:07UTC (2:07pm EDT), excerpt

[Note: EWRadar continues to offer real-time updates from the Hut and DFR webcams, and from the REF and NCD seismic webicorders in the open thread below. The EWRadar monitor will be activated as circumstances warrant.]

Report on Redoubt from the Alaska Volcano Observatory

Summary
The 2009 eruption of Redoubt Volcano continues. A lava dome is currently growing in the summit crater, accompanied by intermittent emissions of volcanic gases and minor amounts of ash. Additional explosive events are likely and could send ash to greater than 30,000 feet above sea level. Such a cycle of dome growth and explosive dome destruction may continue for many months. The potential for lahars (volcanic mudflows) and other flooding down the Drift River Valley remains, as does the potential for trace to minor ash fall on communities near Redoubt (e.g., the Kenai Peninsula Borough, The Municipality of Anchorage, and the Matanuska-Susitna Borough, and possibly more distant areas).

Observations
The 2009 eruption of Redoubt Volcano began with a minor explosion of steam and ash just after 13:00 AKDT on March 15. Major explosive events began at approximately 22:40 March 22 AKDT, and since then AVO has recorded more than 19 separate explosions. Plume heights, as measured by radar and confirmed by pilot reports, have exceeded 50,000 feet (15 km) above sea level on multiple occasions. To date, the largest explosion occurred at 05:55 AKDT April 4, lasted more than 30 minutes, and is comparable in size to the largest event of the 1989/1990 Redoubt eruption. [See EWRadar’s composite reflectivity scan of this eruption – Mod]

Three major lahars (volcanic mudflows), on March 23, March 26, and April 4, have inundated the Drift River Valley and its downstream coastal fan. All of these reached the Cook Inlet and affected the Drift River Oil Terminal (DROT). The peak discharge rates of these lahars remains under investigation, but all are considered significant, and the April 4 event may have exceeded the size of any lahar observed during the 1989/1990 eruption. Smaller lahars that did not impact DROT have also occurred.

Several of Redoubt’s recent explosions have resulted in measurable ash fall over populated areas as distant as Delta Junction (340 miles northeast of Redoubt), with more significant ash fall in more proximate areas, including the Susitna Valley, the Kenai Peninsula and the Anchorage bowl. On the afternoon of March 28, ash fall in Anchorage closed the airport from 17:00 until 07:00 the next morning (March 29). The maximum ash fall measured so far in a populated area is about 1/16th of an inch (1.5 mm) near Seldovia following the April 4 explosion. A measurement of about 1/8th of an inch (3 mm) following the explosion on March 26, was recorded near Silver Salmon Creek Lodge, about 30 miles (48 km) south of the volcano. Trace ash fall has also been observed between explosive events during times when the volcano is emitting a continuous low altitude (< 15,000 feet ASL) gas and ash plume.

A rich variety of seismic signals have been recorded at Redoubt throughout the eruption and in the preceding months of unrest. These seismic events include: (1) typical “rock-breaking” earthquakes; (2) volcanic “tremor”, indicative of steam and other volcanic gases or fluids vigorously propagating through cracks; (3) large, far-reaching, “cigar-shaped” signals resulting from volcanic explosions; (4) ground shaking from lahars as they pass nearby seismometers; and (5) small, repetitive, self-similar events associated with the slow extrusion of lava (this kind of extrusion is often referred to as “dome building”). More than 1700 earthquakes have been located since mid-January, and many more occurred that were either too small or of such a character as to make location impossible. Typically, the magnitudes of these events are small, the average being around M0.5. However, on April 9 a magnitude ML 3.3 earthquake occurred about 2.5 miles (4 km) E/NE of Redoubt’s summit, possibly resulting from a crustal adjustment to the ongoing withdrawal from Redoubt’s subterranean magma reservoir.

Since the fall of 2008, AVO has flown 13 gas measurement flights, and of these, 5 have occurred since the eruption began on March 15, 2009. Elevated carbon dioxide (CO2) emission rates (up to 2000 tonnes/day) were measured in October-November, 2008. Starting in late January 2009, and coincident with a strong increase in seismicity, gas emission rates rose to a level (> 5000 tonnes/d) suggesting significant unrest at the volcano, and emissions stayed at this level until the eruption began. Since that time, emissions of both CO2 and sulfur dioxide (SO2) have been very elevated, sometimes reaching levels in excess of 10,000 tonnes/d. These volcanic gas emission rates are among the largest ever measured in Alaska, though such high values are consistent with an openly degassing volcanic system that is actively extruding lava. Based on measurements and observations from Redoubt’s previously observed eruptions, these gas emission rates are likely to drop substantially when the eruption wanes.

The combination of gas and ash emission from Redoubt since the beginning of the eruption has on occasion resulted in a brownish-yellow volcanic haze in the Cook Inlet region. The volcanic haze contains small quantities of ash, water vapor, sulfur aerosols, and liquid droplets suspended in the air. The main concerns for human health in volcanic haze consist of ash, sulfur dioxide gas (SO2), and sulfuric acid droplets (H2SO4), which forms when volcanic SO2 oxidizes in the atmosphere. Volcanic haze can be both an eye and respiratory irritant. The State of Alaska Epidemiology Bulletin No. 5 summarizes the health effects associated with volcanic emissions and is available on the web at: http://www.epi.hss.state.ak.us/bulletins/docs/b2006_05.pdf.

Visual and satellite observations show that by March 27, a deep crater about ½ mile (800 m) across formed in the middle of the summit amphitheater, likely from one or more of the explosions during the early stage of the eruption. By April 4, a north/south elongated lava dome, about ½ mile (800 m) long had grown out of the new crater, at an elevation of around 8000 feet (2400 m) above sea level. Most if not all of this dome was destroyed during the large explosion of April 4. A large amount of ice and snow has been removed from the upper Drift Glacier. The Drift River Valley has also been mostly denuded of snow and is covered with lahar deposits. The latest observations, as of about April 9, show a growing lava dome in about the same place as the previous dome. This new dome is about ¼ mile (400 meters) in diameter, and roughly circular as viewed from above.

Prognosis and Ongoing Hazards
The 2009 Redoubt eruption began with a series of large explosions on March 22-23, followed by less-energetic dome growth in the summit crater. On April 4 another large explosion occurred, which was in turn followed by growth of the current dome. There will likely be additional explosive events during the coming days to months, but their exact nature, as well as timing, remains uncertain. Because the dome sits at the lip of a steep slope leading out of the crater it can become unstable, and (as in 1990) collapse into the Drift River valley, producing avalanches of hot lava blocks, pyroclastic flows, lahars, and ash columns tens of thousands of feet tall, which can carry ash to Alaska communities. During periods between explosions, residents and pilots may also notice occasional sulfur smell and hazy conditions due to low-level ash and volcanic gas emissions

Status of Instrumentation and Observation
Monitoring capabilities at Redoubt remain strong. The real-time network consists of 7 seismometers, a pressure sensor, and 2 web cameras. There are 4 additional seismometers, 3 additional GPS receivers, and 1 time-lapse camera that record and store data on site. Two seismometers and a continuous Global Positioning System (GPS) receiver were damaged by lightning discharge during the March 23 explosion and are not currently operational. Repair of the damaged real-time instruments and collection of data from instruments with on-site recording will occur as weather and safety conditions permit.

Redoubt is also monitored by satellite. Observation flights for airborne gas measurements, targeted thermal imaging, geologic analysis, and sampling of eruption deposits are also made, again, as weather and eruption conditions permit.
The Alaska Volcano Observatory is staffed 24/7 and will remain as such so long as conditions warrant.

Last weekend’s cold, windy end to a run of nice spring weather was due to this low pressure cell, moving into the Great Lakes from the US midwest. It dumped upwards of 8″ of lake effect snow on parts of the Chicago area and gave the GTA a reminder of the winter of 08-09, with blustery lake effect snowy days from the cold NW flow on its back side. We went from shirt sleeves and BBQs on Sunday, to boots, mitts and gloves on Monday.

We don’t always get to see a nice tight rotation like this over us. Pressure got down as low as 992 hpa and it dropped about 50mm of rain out of the warm sector (leading east edge) before flipping over to woolly time (the low is much larger than what is shown – this radar site’s range is only able pick out the core of the low. Usually we see only air motion in one direction as the radar samples a portion of the low away from the core.

Northern hemisphere low pressure cells are counter-clockwise rotating cyclones, where high pressure areas rotate clockwise and are anti-cyclones.

If you watch the video and think about it a minute, you can see how the leading edge of the low draws warmer air from the subtropics , and the back side pulls down colder arctic air. The mass of colder air being slowly pulled down produces the drier “cold front” rotating around the center of the low, pushing up against the warmer air dragged up from the south.

Ahead of this cold front the air is moist and turbulent, leading to the active weather we experience. As the cold front rotates past us, the drier air gives rise to clearer skies (drier air) and cooler temperatures.

Air being pulled into the low (low pressure because the air at the center is moving upward) causes the strong winds we experience, as the low and fronts pass. In contrast, Highs pull dry air down from the upper atmosphere. This air being drier, doesn’t have water to condense and form clouds, hence the clear, but ofter cooler days.

I’ve added a new display mode for EWRadar: MIXED. This mode is intended to cover weather patterns associated with mixed precipitation. NEXRAD radar can’t distinguish precipitation type for the standard radar display patterns. Standard NWS colours tend to logically suggest rain patterns (they are also chosen to accommodate issues of colour blindness) rather than snow or mixed precip.
I have a snow colour array for winter use but it didn’t seem right for mixed either. Typical televised presentation denotes blues for cold/snow masses, green for warm/rain masses, and purple (ok, mauve) for the boundary areas between the two sectors. This is not derived from the radar product – this is a graphic produced by the commercial weather service providers for television.

Therefore I have created a colour array that displays mauve up to 25 dbZ, blues through to 45 dbZ, and the usual reds thereafter. When this display is up, you can assume that precipitation modes in the region may be rain, snow or mixed, including (but not necessarily) freezing rain, depending on local factors and influences.

The display field will be marked “Mixed precip mode” and the tagline will indicate “MIXED” as well, when the mode is in place. Alert features remain the same as with the other modes.

EWRadar now has a Youtube channel: www.youtube.com/user/EWRadarProject/

I’ve put two time-lapse scans up of this morning’s eruption at Redoubt:

Mt Redoubt Apr 04/09 Eruption Composite radar scan
and
Mt Redoubt Apr 04/09 Eruption Echo Tops radar scan

One is a time-lapse of the “Echo tops” scan, measuring altitude, and the other is the “short range composite” giving an overall picture.

2013-06-01: Note: page needs updating – some links have changed. For the AVO’s excellent site, follow the observatory link in the text below.

NOTE: January 5/10: Due to reduced seismic activity, alert levels are reduced to green again.

NOTE: The Alaska Volcano Observatory has issued an alert upgrade to yellow due to increased seismic activity at the volcano…
See monitors below (all monitors now up…)

2009-12-28 12:37:19 – Status Report:
Earlier this morning, AVO elevated the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY at Redoubt Volcano. Beginning about 4:00 pm AKDT on December 27 (0100 December 28 UTC), small repetitive earthquakes began to occur in the vicinity of the volcano’s summit. Activity is continuing this morning; these earthquakes are very small and have decreased in frequency overnight. These earthquakes represent a departure from seismicity at the volcano over the past five months. (See http://www.avo.alaska.edu/webicorders/Redoubt/RSO_EHZ_AV.php). Clouds currently obscure web camera and satellite views of the volcano.

These earthquakes could be precursory to renewed eruptive activity at the volcano and increased instability of the lava dome. Whether this will result in explosive activity or collapse of the lava dome is unknown at this time. However, there is a heightened possibility of volcanic activity that would produce a volcanic ash cloud and associated ash fall, pyroclastic avalanches, and lahars and flooding down the Drift River.

AVO is monitoring the situation closely and will attempt to overfly the volcano when weather allows.

NOTE: October 1/09: The Alaska Volcano Observatory has lowered the status of Mt. Reodubt to green-normal, indicating that the volcano has returned to its pre-eruptive state. The AVO will continue to monitor Mt. Redoubt for activity. Ephemerata Weather Radar will keep the active monitoring link open, as the seismic webcorders are maintained and EWR monitors them in real-time in the blog page.

NOTE: July 1/09: The Alaska Volcano Observatory has lowered the status of Mt. Reduobt to yellow-advisory. While seismic activity remains above background, dome growth has slowed substantially, and while there still remains a risk, its believed at this time to be much lower. Check with the AVO site linked below.

NOTE: May 5/09: The seismic stations are showing increased low level activity. The dome is growing and there remains concern that it may explosively erupt. The AVO reports that the seismic signature is similar to that which preceded the March and April eruptions.

NOTE: Apr 19/09: Webicorder REF appears to be back online, but so too is RSO, so I’ve swapped in RSO. Webicorder RSO, closest to the volcano, was damaged in one of the first eruptions, but has been recently serviced. RDN is believed to be buried in snow, and has a poor trace. Rather than noting changes each time, I’ll simply update the trace info below according to which is running well. All are presently accessible in any case. Redoubt is still condition “Orange-Watch” and dome-building continues. EWRadar is offline while things are quiet.

NOTE: Apr 17/09: Webicorder REF is still having difficulty, so I’ve swapped it out with NCD (AVO has crews in the field today – perhaps REF is being messed with). NCD is not quite as sensitive, but is giving a steady trace. Both are still available in the text line below the display.
__________

Redoubt Volcano is approximately 109 miles east of Anchorage, Alaska, on the north shore of Cook Inlet, and about 135 miles east of Wasilla. It lies at the head of the Drift River Glacier. The Drift River oil terminus is at the inlet at the outflow of the Drift River Valley. Lahar flows (icy ash flows) have reached the oil terminal buildings, and pose a threat to the terminal facilities. Plans are being made to off -load a quantity of the oil currently in storage at the facility.

The small, shallow repeating volcanic earthquakes indicative of lava dome growth that continued at the rate of 3-4/minute the last few days, subsided, then resulted in a strong eruption this morning at 6am AKDT (1400UTC). as can be seen on station REF.

The webcams HUT and DFR below and the station REF seismic trace following, are continuously updated from the Alaska Volcano Observatory site. The radar scan is assembled from NWS data by Ephemerata Weather Radar – refresh browser as desired for most current information. The seismic trace will give an indication of possible impending eruptions by its increased activity.
__________

A sunrise view of the Apr 04/09 eruption from the Hut webcam is immediately below. A composite reflectivity radar time-lapse scan, annotated, is here: April 4th eruption. There are several images below the active monitors and a link to the AVO image gallery.

Sunrise on the Apr 04/09 eruption of Mt. Redoubt, from the Hut webcam

Sunrise on the Apr 04/09 eruption of Mt. Redoubt, from the Hut webcam


__________

Hut Webcam (Online):

Webcam is presently offline from AVO
(Refresh for most recent webcam image. Sunrise is +/- 8am AKDT, 12Noon EDT, 16UTC, sunset 12 hours later).

DFR Webcam (Online):

Webcam DFR is presently offline from AVO
DFR webcam is 12.2 km NE of Redoubt, and takes a picture approximately every 2 hours.

RSO_EHZ_AV Webicorder* (Online):

Webicorder update is presently offline from AVO
Webicorder RSO_EHZ_AV 24hr. (refresh for webicorder update – Active trace is the very bottom one).

NCT_EHZ_AV Webicorder* (Online):

Webicorder update is presently offline from AVO
Webicorder NCT_EHZ_AV 24hr. (refresh for webicorder update – Active trace is the very bottom one).

RDN_EHZ_AV Webicorder* (Online):

Webicorder update is presently offline from AVO
Webicorder RDN_EHZ_AV 24hr. (refresh for webicorder update – Active trace is the very bottom one).

REF_EHZ_AV Webicorder* (Online):

Webicorder update is presently offline from AVO
Webicorder REF_EHZ_AV 24hr. (refresh for webicorder update – Active trace is the very bottom one).

( Alternate webicorders are Webicorder NCT_EHZ_AV, Webicorder RDN_EHZ_AV and Webicorder REF_EHZ_AV . Webicorder updates and Hut views courtesy of AVO/USGS. )

Its important to note that the seismic instruments also detect earthquakes and other tremors not directly associated with Redoubt eruptions. In some cases, it takes a bit of work for AVO and USGS staff to determine if a seismic signature signals an impending volcanic event, or whether it is a collateral signal from a different event. Earthquakes are common in the Pacific rim Ring of Fire zone.

  • A webicorder is a software interface for a modern digital seismic instrument that produces a visual “chart trace” like those produced by the original drum chart pen recorders. Seismic instruments measure the vibration in the ground from tremors, earthquakes, eruptions, etc. They may also be influenced by vehicles, wind, and, in Alaska, passing bears and Democrats.

EWradar scan: (Offline) (Redoubt Volcano is centered in the blue circle across Cook inlet from the Kenai radar station. For scale,the circle has a diameter of 12 miles, the distance from the volcano to Kenai is 38 mi.):

Radar scan is presently offline from Ephemerata Weather Radar
_______

These are some of the many spectacular images of Mt. Redoubt in the Alaska Volcano Observatory image gallery.

Redoubt, as seen on the morning of April 16, 2009, from Cape Starichkof (~ 5 mi north of Anchor Point), Kenai Peninsula. April 16, 2009 08:18:00 ADT. Photograph courtesy of Dennis Anderson.

Some context - Redoubt, as seen northerly across Cook Inlet on the morning of April 16, 2009, from Cape Starichkof (~ 5 mi north of Anchor Point), Kenai Peninsula. April 16, 2009 08:18:00 ADT. Photograph courtesy of Dennis Anderson.

Photograph of Redoubt Volcano in eruption taken during observation and gas data collection flight on March 30, 2009. View is to the east. Continuous emission of volcanic gas, water vapor, and ash is producing a plume rising to about 10,000 to 15,000 feet above sea level. AVO scientists observed ash falling up to 25 miles downwind, and Anchorage has received a light dusting. Game McGimsey, Image courtesy of AVO/USGS.

Photograph of Redoubt Volcano in eruption taken during observation and gas data collection flight on March 31, 2009. View is to the east. Continuous emission of volcanic gas, water vapor, and ash is producing a plume rising to about 10,000 to 15,000 feet above sea level. AVO scientists observed ash falling up to 25 miles downwind, and Anchorage has received a light dusting. Game McGimsey, Image courtesy of AVO/USGS.

 View to the northwest of ash deposits on the upper Drift River valley and surrounding terrain from recent eruptions of Redoubt volcano. Game McGimsey, Image courtesy of AVO/USGS.

View to the northwest of ash deposits on the upper Drift River valley and surrounding terrain from recent eruptions of Redoubt volcano. Game McGimsey, Image courtesy of AVO/USGS.


____________

Nice bit of video assembled by Bretwood Higman from March 27. It consists of 15 sec stills framed up. The large explosion is the 7:25 (AKDT) eruption.

Redoubt Eruption March 27 2009 from Bretwood Higman on Vimeo.

Redoubts 1:40 pm, March 28 eruption, as captured by Dennis Anderson

Redoubt 15:29 eruption, 3/28/2009., courtesy Rick Monyahan

Lightning from Redoubt 11:20 pm, March 27, eruption, courtesy Bretwood Higman.

Lightning from Redoubt, 11:20 pm, March 27, eruption, courtesy of Bretwood Higman.

Redoubt volcano from the south over the ash-covered Crescent River Valley.

Redoubt volcano viewed from the south over the ash-covered Crescent River Valley.

March 26, 2009. Game McGimsey, Image courtesy AVO/USGS.

Some past events:

The April 4, 2009 eruption was one of the more dramatic eruptive events. This EWR composite shows the eruption as it appeared on radar:

“2009-03-27 01:59:09
Seismicity associated with the explosive series of eruptions that began at 11:47PM AKDT has tapered off to low-level tremor. The volcano remains restless and seismicity is still above background. The aviation color code remains at RED.” Alaska Volcano Observatory

ahg_20090327_0832_net

This scan from 08:32UTC shows Redoubt erupting. Echo Tops reports altitude to at least 45,000 feet (red). Ash cloud is moving eastward towards Kenai in subsequent scans: (09:33UTC):

ahg_20090327_0933_net

Alaskan volcano Redoubt has been lowered to status “Orange – Watch”. Seismic activity has reduced to frequent low amplitude volcano-associated quakes which, according to the Alaska Volcano Observatory, is consistent with the buildup of a dome in the cauldron, and venting is mostly steam with light ash production. Domes are considered inherently unstable, and may result in an explosive eruption, due to their capping effect.

The open thread below will continue to take updates from the AVO from its seismic webicorders and the two mountain placed webcams. EWRadar monitoring has been suspended for the time being, but will resume if the circumstances warrant.

Update 1: We’re off and running again! Approximately 14:05 UTC (10:04 EDT) Redoubt blew again. EWRadar is back up in Tops mode tracing the eruption. The webcams won’t likely be visible for a couple of hours as its still dark at Redoubt, local daybreak being about noon EDT. Check in with the active monitoring thread just below.

Update 2: 10:47EDT: EWradar is tracing a large eruption. At 10:18 EDT plume exceeded 45,000 feet, and there is a large downwind ash trace to the SE developing.

Update 3: Webcams have now been turned on.

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