"New" Mexican Volcano Caused by the Oaxaca Earthquake? Not Likely.

By Erik Klemetti
March 23, 2012 |

This week saw a very strong earthquake in an area of southern Mexico – a M7.4 event centered 25 km from Ometepec. It looks like it was a relatively shallow earthquake (~15 km) that was related to thrusting due to the subduction of the Cocos plate under Mexico. Although this earthquake was larger than we might expect in Mexico, it is in a zone of high earthquake hazard, so the earthquake itself was not surprising – remember, subduction zones and earthquakes go hand in hand. The effects of the earthquake on the area have been significant, with over 1000 building collapsed or damaged, but thankfully few lives were lost.

After the earthquake, there has been a flurry of news in Mexico about a supposed "new volcano" that appeared between Huajintepec and Huixtepec municipality of Ometepec. The details are scant, but the mayor of the district claims the new volcano to be "tiny" (but in other articles, he says the "volcano" has been there "for many years"). As usual, there is a lot of misleading coverage, like this story that shows a picture of an undersea vent at NW Rota 1 in the Marianas Islands (with no caption to say so). There is also a lot of speculation in the Mexican media that the "new volcano" might somehow have caused the earthquake or all the aftershocks being felt in the region.

Now, there are quite a few reasons why it is very unlikely that there is a "new volcano" formed by the Oaxaca earthquake or that the earthquake was somehow caused by this supposed volcano.

First, why this earthquake didn't cause a "new volcano": Although volcanoes in subduction zones are common, the location of volcanoes is not arbitrary. This is why we get ranges of volcanoes. The Cascade volcanoes in the U.S. all occur well inland from the actual point where the Juan de Fuca plate subducts under North America (the "trench). If we look at the active volcanoes of Mexico (below), the volcanic arc is almost 300 km from Ometepec, so the likelihood a new volcano would occur there has a very low probability (next to zero) – you have to go a long way from Ometepec to find active volcanoes. Some articles have been comparing this to the emergence of Parícutin in 1943 – a case of an actual "new volcano", but Parícutin is smack in the middle of the active volcanic belt. To get magma to form, melting of the mantle has to occur and in subduction zones, to do that, you need water to come off the oceanic crust that is being pulled under the overriding plate. The water only comes off at a certain depth (which is related to temperature), so the location of the volcanic arc tends to be hundreds of kilometers from the trench (however, it varies from subduction zone to subduction zones based on the angle of the slab beneath the overriding plate).

The active volcanic arc in Mexico (red triangles). Ometepec, close to the epicenter of the recent M7.4 earthquake is marked - and over 275 km from any active volcano.

Second, why any "new volcano" can't be the source of the seismicity in Oaxaca: Whenever geoscientists examine earthquakes, we look at how the earth moved along the fault. This produced the famed "beachball" diagrams of the focal mechanism of an earthquake. For earthquakes generated by magma rising under a volcano, we want dilation/extension as the crust moves out of the way to let the magma through. The Oaxaca earthquake had a reverse/thrust motion, meaning that the force was compressional, not dilation. This sort of motion is not consistent with magma movement and is very consistent with thrust faulting due to the subduction zone. The many aftershocks from the earthquake are highly common from any large earthquake, so a "new volcano" is just not necessary to explain the 80+ aftershocks felt so far.

So, all this "news" about a new volcano in Mexico is likely the product of media hysteria after a disaster. The only actual "observations" I've seen is claims of "hot water gushing/bubbling" after the Oaxaca earthquake, but hot springs are common along faultlines in many locations around the world. This doesn't mean that magma near the surface is the source of heat, but hot water will follow faults to reach the surface. A new earthquake might open new pathways for this water. However, with such scant information, it is hard to say that even that is happening near Ometepec. What I can safely say is that a "new volcano" is not very likely at all, both in causing the earthquake or being produced by the earthquake.

http://www.wired.com/wiredscience/2012/03/new-mexican-volcano-caused-by-the-oaxaca-earthquake-not-likely/

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Zone C closed: Reports of Increased seismic activity at Soufriere Hills Volcano

Posted on 23 March 2012.

by B. Roach

Appearing immediately below is the weekly report we received at mid-morning today from the Montserrat Volcano Observatory – Weekly Report for the period 16 to 23 March 2012.

Activity at the Soufrière Hills Volcano is low, although seismicity has increased.

The seismic network recorded nine rockfalls, one hundred and five volcano-tectonic (VT) and four hybrid earthquakes. Two swarms of VT earthquakes have occurred, one between 16:04 and 16:51 hrs on the 22 March with 49 events and another between 03:10 and 05:27 hrs on 23 March with 54 events. Earthquakes in the second swarm were markedly larger than those in the first.

The average sulphur dioxide measurement this week was 433 tonnes per day with a maximum of 654 and a minimum of 282 tonnes per day.

Observations on the morning of 23 March showed several changes on the volcano. Steam venting (Fumarolic) activity on the volcano has increased and a new steam vent (fumarole) has appeared on the northwest face of the lava dome behind Gages Mountain. A pulsing steam vent containing a small amount of ash has formed in the back of the February 2010 collapse scar. Very light ashfall is occurring on the western flank of the volcano. Audible roaring associated with the venting can be heard intermittently from MVO, 5.75 km NW of the volcano.

Pyroclastic flows can still occur at any time without warning. Lahars (mudflows) remain a hazard. Tracks across the Belham valley are frequently destroyed or heavily modified by lahars, therefore caution should be exercised crossing the valley during and after rainfall.

The Hazard Level is 2, however until further notice there is no access to Zone C. Maritime zone W remains daytime transit only (boats may sail through the zone but must not stop).

The MVO weekly report is sent out every Friday by mid-day.

But, it has been the habit for a long time now for the MVO to send to The Montserrat Reporter (TMR), nothing else in connection with the volcano except for the weekly report. It was on this background we received the following release at mid-afternoon which reads as follows:

"A noticeable increase in seismic activity at the Soufriere Hills Volcano resulted in a closure of Zone C, which had been reopened for daytime entry in December 2011.

Director of the Montserrat Volcano Observatory (MVO) Dr. Paul Cole said on ZJB Radio Montserrat on Friday morning that it was a precautionary measure as they continued to monitor the volcano, which has been relatively quiet since early 2010.

By early afternoon the MVO released a statement noting that mild ash venting had begun and was emanating from the 11 February 2010 collapse scar.

MVO photo taken from Jack Boy Hill of the ash vents today March 23, 2012 (supplied with release)

"Following two volcano-tectonic (VT) swarms on the 22 and 23 March 2012 involving 49 and 54 events respectively, mild ash venting began at Soufriere Hills Volcano at around 8:00 am local time on 23 March. The venting was sourced from the floor of the 11 February 2010 collapse scar, immediately south of the old English's crater wall and to the west of the long-lived hottest fumarole previously identified. Fumarolic activity on the volcano on the morning of 23 March increased markedly and a new steam fumarole was identified on the NW side of the dome immediately behind Gages Mountain," the statement read.

"The ash venting was clearly pulsatory and sent ash to approximately 6000 feet above sea level (3000 feet above the volcano). At its peak, black jets of ash were seen rising a few hundred metres above the floor of the collapse scar. This type of activity is probably 'phreatic' in origin and is formed where superheated rock meets groundwater causing the rocks to fragment, generating ash.

"VT earthquakes are related to fracturing rocks probably as a result of increases in pressure. It is likely that these pressure increases and the resulting earthquakes are related to uprising magma below the volcano. Similar types of activity have occurred at Soufriere Hills Volcano up to several months prior to restarts in magma extrusion, for example in 2005 and 2008," the MVO statement ended.

Zone C which comprises of Cork Hill, Weekes, Foxes Bay, Richmond Hill, Delvins and extending 500 m out to sea is part of the Exclusion Zone. It was reopened in December 2011 after the hazard level was lowered from 3 to 2, which made daytime access possible in those areas. Dr. Cole says there are no plans to raise the hazard level but that the area would be closed off and the gates locked."

http://www.themontserratreporter.com/featured/reports-of-increased-seismic-activity-at-soufriere-hills-volcano

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Authorities lower alert level for remote Alaska volcano

By Associated Press, Published: March 23

ANCHORAGE, Alaska — The alert level for a remote Alaska volcano has been lowered for lack of activity in the past 10 days.

The center in a release says there have been no explosions detected since March 13, and there's no evidence the lava dome has grown in that time.

The center says there are no significant deposits of ash on the volcano, suggesting earlier eruptions might have been relatively ash-poor.

Cleveland is a 5,675-foot peak on an uninhabited island 940 miles southwest of Anchorage.

Authorities say sudden eruptions still could occur at any time, and ash clouds 20,000 feet above sea level are possible.

http://www.washingtonpost.com/national/authorities-lower-alert-level-for-remote-alaska-volcano/2012/03/23/gIQAdx5GWS_story.html

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Popocatepetl 22 exhalations emitted in the last hours

22.03.2012

The National Center for Disaster Prevention (Cenapred) reported that the volcano Popocatepetl has had 22 low-intensity exhalations accompanied by emissions of water vapor and gas in the last hours.

Through a statement, the agency of the Ministry of the Interior (Interior Ministry) explained that the exhalations of major importance occurred yesterday at 12:31, 13:04 and 13:12 hours today at 01:05 hours.

He noted that there were five earthquakes of low magnitude volcanotectónicos segments spasmodic tremor of low amplitude which totaled approximately nine minutes.

He stressed that the other parameters remain unchanged monitoring important.

The Cenapred said that during Wednesday night that the filament was observed in the crater of the volcano had increased from 20:00 hours and until the last report there is a continuous emission of steam and gas.

He noted that currently the volcano can not fully appreciate due to cloud cover prevailing, therefore, the light of volcanic alert remains in Phase 2 yellow.

He said that provides moderate exhalations, some with ash emissions, sporadic bursts of low to moderate probability of emission of incandescent fragments within walking distance of the crater and incandescent light in the observable crater overnight.

The agency called on the authorities concerned to continue the safety radius of 12 kilometers, so staying in that area is not allowed and suggested keeping the controlled traffic between Santiago and San Pedro Nexapa Xalitzintla via Paso de Cortes.

Civil Defense also asked to maintain preventive procedures, according to their operational plans and the attentive public to official information.

http://www.cronica.com.mx/nota.php?id_nota=647528