[Bazmundo]

This looks bad*, the Hierro volcano, the (least studied) SWrn-most of the Canary Islands, has undergone renewed activity since July - but in the last few days has seen a huge increase in the number of >2mag quakes. I'm no expert on these matters but it looks like a swarm.

Extract from the Global Volcanism Program/USGS activity report:

Quote

HIERRO Canary Islands (Spain) 27.73°N, 18.03°W; summit elev. 1500 mInstituto Geográfico Nacional (IGN) reported more than 900 new seismic events at Hierro during 20-26 September, five of them felt by residents. The maximum magnitude recorded was 3.4. The total number of located events had reached more than 8,100 since the anomalous activity began on 16 July. The rates of both GPS deformation and seismic energy release had significantly increased during the previous seven days. On 23 September, the Canarian Autonomous Government raised the Alert Code to Yellow.

Geologic Summary. The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive Hierro shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided 1500-m-high scarp towers above a low lavaplatform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and south at 120 degree angles form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an historical eruption in 1793.

Map

Source: Instituto Geográfico Nacional (IGN)


Hierro Information from the Global Volcanism Program

Some links I've discovered on the IGN pages (translate needed):
Hierro Updated Summary - various charts of eq loc and depth, accumulated energy, etc.
Earthquakes last 10 days (Canary Islands)
Seismic signals (all sites)
Latest IGN News

* I say it looks bad because of the repercussions of a slump or landslide.

[Dave K]

Another site (Spanish/English/German language): http://www.avcan.org/

It's making the popular press (ignoring the Daily Fail which has it also)

http://www.telegraph.co.uk/news/worldnews/europe/spain/8795750/Volcano-threat-sparks-evacuation-in-Canaries.html

[ldavidcooke]

Hey Baz,

What makes it even worse is the subterranian dykes holding vast pools of water. It will not require surface volcanic activity to heat the water sufficently to possbly result in slope failure. The complication is the only true measure would be to monitor the deep soil temperature (roughly depths of 100 meters) and ground fracture widths. The potental of this event is one of the reasons I will not live or work East of the Piedmont Ridge 15 miles East of Alamance County in NC. I know it is alarmist; however, based on the evidence I had seen about 25 years ago it was clear this was the most likely endangering natural disaster the East coast of the US has. Yet, I was not alarmist enough to insist my Florida family members do likewise.

[Bazmundo]

Weather and webcam for Hierro and Las Puntas (town on the north shore): http://meteolaspuntas.es/

More weather and seismicity info: http://www.laspuntas.es/

Static Webcam Image (needs refreshing), also available here.

[Bazmundo]

ldavidcooke, on 30 September 2011 - 13:35, said:

I know it is alarmist; however, based on the evidence I had seen about 25 years ago it was clear this was the most likely endangering natural disaster the East coast of the US has. Yet, I was not alarmist enough to insist my Florida family members do likewise.

Hey Dave,


I'm just reading through this: http://www.lapalma-t...om/tsunami.html

[John Mason]

Baz, David - that site Baz linked to does remind me somehow of certain sites that take a certain stand WRT climate change, vaccination, evolution etc!

However, to connect activity including quake-swarms to a major quake/displacement/gravity-slide is likely a little premature, too. As we say on the warnings-team here, it might merit a Watch - and that would be for the broad gamut of volcanogenic effects.

Cheers - John

[Bazmundo]

John Mason, on 30 September 2011 - 14:07, said:

Baz, David - that site Baz linked to does remind me somehow of certain sites that take a certain stand WRT climate change, vaccination, evolution etc!

However, to connect activity including quake-swarms to a major quake/displacement/gravity-slide is likely a little premature, too. As we say on the warnings-team here, it might merit a Watch - and that would be for the broad gamut of volcanogenic effects.

Cheers - John

That site does link to some fairly reputable sources though, I'm looking around for any neutrals. I think it's the TV documentary and exaggerated modelling it has issues with, not the original research.

I actually preferred the statement from the Spanish National Geographic Institute on their alert: " ...should be prepared for an unfavourable outcome of this phenomenon". (might just be Google translate though)

[John Mason]

NOAA/USGS should be fairly reliable on this too if a situation starts to develop.... I imagine they are all in contact with one another.

Cheers - John

[Bazmundo]

The Geology Of Spain - Teresa Morenoa PhD, Wes Gibbons (Geo. Society of London, 2002); is in favour of catastrophic collapse potential.

[Andrew Cole]

All that stuff about La Palma seems sensationalist to say the least!

But we're talking about different islands right? I haven't seen anything suggesting similar research has been done on Hierro?

Andy

[Bazmundo]

Geophysics of the Canary Islands (Peter Clift, Juan Acosta, 2005) is somewhere inbetween: "...it is possible that the landslides are not solely the creation of avalanches, but are constructed by both debris avalanche and debris flow processes... ...these sediments were deposited by repetitive failures". It also states that some debris runout distances from Canary Island debris 'avalanches' extend 12 to 95km and have volumes between 50 and 800km³.

In any case, as you say John, these are tectonic effects and the outcome of the recent quakes could be of any kind. Certainly getting interesting though!

Edit - just found European Margin Sediment Dynamics (Jürgen Mienert, Phillip Weaver, 2003) with side-scan sonar and seismic imagery for Hierro. It also favours 'catastrophic debris avalanches' specifically for Hierro, but calls them 'relatively superficial'.

[ldavidcooke]

Hey All,

If I look at an elevated surface and there are fissures running parallel with the plane of the ocean then I am inclined to believe the potential of slope subsistance is possible. That it is stable in the absence of tectonic/geologic activity would support an assumption that the fissure may have a relationship to geologic processes and not erosion. That large pools of subterrain water exist supprort the conclusion that the surrounding material is not as porous as may be indicated.

Given just these two elements the potential for a slide or avalanche is a possibility. The issue, IMO, is whether the hypothesis and indicated weakness demonstrates a correlation in the historic record and the conditions surrounding supportive evidence.

IE: If the date of the last failure were in the period between 17 and 10kya the probability of low hydrostatic pressures could support the failure due to a simple change in the statics or CG of the slope face.

If there are ranks of parallel fissures the indications would be that a stable static condition was established. If on the otherhand that there is only one or two fissures exist on a face then there could be sufficient stress or potential KE for further failure. The slope height where the fissure is located, its depth and the area between the fissures suggest the mass PE of a slide/avalanche.

The evaluation of the fulcrum depth suggests the force necessary to displace the mass. If the subterrian pools are very deep it would require a magma charge within, say 300 meters or a few hundred degrees to cause a failure. If the pools are shallow, the magma may not have to get much closss then 1000 meters or a few tens of degrees to cause a failure.

Based on a 1-3km differential it would take more then a rumble or a filling of a magma chamber. It would likely require an immenent erruption which does not appear likely; yet!

[Sam Jowett]

Some interesting discussion of El Hierro on Jon Frimman's volcano blog http://www.jonfr.com/volcano/?p=1563
Sounds like the geology at El Hierro is different to on La Palma and much less likely to generate a large landslide...

[ldavidcooke]

Hey Sam,

Sad to say, most are discarding the gravitational failure near the coast and the thiness of the cone face from the coastal face to the sea floor. As to a failure or not depends on whether or not the magma near the base fills and melts the sills before finding release at the top.

With the angled flow it appears to be more likely to be a sill. Hence the next question is the sill wall ending above the sea floor or above. Current depths of activity point to below. This suggests that any release will be near the cone peak.

As to the intensity it is likely related to water intrusion or reserves in the sills above the magma. Being more of a "sheild" or interspaced angled sills coupled with slope failure would suggest the upper level would have a very different water pool character then La Palma; however, gravitational failure or "stair stepping" does point to potential edge failures though with most above sea level.

If the sea level were 100-300 meters shallower the potential of a coast failure would increase. So though the geologic character is different the potential is not terribly different, though the mechanics and magnitude of the potential is much less based on the evidence we have seen so far.

[Bazmundo]

Tremors at Hierro show it was grumbling away through the latter part of Sunday.

Attached thumbnail(s)

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[ldavidcooke]

Hey Baz,

I just had an interesting thought. Having grown up on the coast and living just off the beach for one year I have seen some interesting responses of the land/sea interface. Over on RC a fellow wrote in looking for a photo for the cover of his book wrt sea level rise. Dr. Schmidt suggested a photo of a storm washed out home on the Barrier Is. here on the NC coast. (Of course my mind immediately jumped to a partially buried tide gauge, calling it a "Stick in the Sand".) The funny thing is it got me to thinking, I remember after a particularly bad storm in 1960. The house behind ours was 6 meters above Sea Level, yet, after the Storm, it washed out the sand under their pool house.

The thing that really caught my eye was the pool and ridge that formed between the failed pool house and the surf. Going further I extended this thought to the formation of the Outer Banks and Florida's Merit Island. Both are about the same age and under going similar erosion. Only more rapidly here in NC due the slightly higher tides.

The point is though they claim there is no evidence, I am curious if both these features, 1000km separate, could have similar origins. It is within the realm of possibilities these features, the Sand Hills and South Carolinas Low Country (Lake Moltre/Santee complex) could all be related features of a large tidal wave. Be curious to see how this plays out as the Sand Hills and Santee Lake are roughly 200km inland. A heck of a displacement to reach that far inland, though if weighed down several 10s of meters by glaciation, not unbelieveable.

[Chris Alder]

Just booked a week off in the middle of October and flight schedules from bmth airport are good for spending a week in La Palma, would be nice to be close to any potential action

[Chris Alder]

Looks like a submarine eruption has begun a few km's south of El Hierro water between 500 & 1000 metres deep. Nothing officialy confirmed yet however there is talk that the eruption could migrate from being fissure in nature at the moment to an above surface eruption within the next few hours/days.

[Bazmundo]

Statements on FB from AVCAN and INVOLCAN read as though it's a gas vent, and that no surface evidence for a submarine eruption (after an inspection by helicopter from the National Guard) is present. All agree the next 48hrs are crucial for developments.

http://www.facebook....AN/163883668446

MODIS just missed Hierro today, but the ESA's MERIS instument can see sediments offshore of W Africa and doesn't pick up anything around the island at 1130-50z:
http://hse-meris1.eo..._image_0260.jpg - (19.2mb jpg)

[ldavidcooke]

Hey Chris,

The basic physics would not support a aerial release. If the containment of the magma column has been breached the lava will follow tbe path of least resistance. The amount of force required to breach 500m of rock as opposed to the pressure exerted by 500 m of water would suggest the erruption remaining submarine. Even if the magma were in the column within meters of the aerial release the combination of weight and pressure in the column would likely result in a submarine erruption.

This goes slong with the earlier suggestion I made. If the sheild had been weakned by earlier avalanches or shelf/dyke collapses it was more likely for a side or lateral eruption. That this could result in an undermining of the shield plate above is a good possibility. I would carefully monitor the land covering above the lava tube vent to insure the was not the possibility of failure.