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Earthquake!

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A couple of days ago we witnessed a series of pyroclastic flows, and this morning it was an earthquake. I was out on the deck of the cabins. The cabins are on stilts but stand firm against the worst wind and rain that Costa Rica can throw at them. However, the structure had what could be described as an unnatural quiver - almost as if the wind had caught it in an unusual way. Except there was no wind.

Others felt it and after breakfast I checked online. The USGS are recording a Mag.4.8 earthquake at 9.894N  85.272W 46.7km deep, "Coast of Costa Rica" (actually locating it just on the Nicoya Peninsula). OVSICORI are giving it a slightly higher energy of 5.1. The differences are probably due to different equipment locations. Also the USGS calculation will be fully automated and as it is only a moderate non-US earthquake, it probably hasn't been examined by a human.

The coastal location means it is NOT an Arenal earthquake but an earthquake related to subduction of the Pacific Plate under the Caribbean plate. The depth is consistent with this - it is too deep for a volcano, and most earthquakes of this depth are related to subduction.

Here's the seismogram recorded by the OVSICORI Volcan Arenal seismometer (VACR):

VACR_seismogram_eq.png

The earthquake is the largest squiggle just after 6:45am local time. The seismometer even goes off scale.  It is only a moderate sized earthquake but we are fairly close, and the seismometer is set to detect vertical motions (the dominant kind in a thrust fault - which is the most likely for a subduction zone).

I've just published all the panoramic photos, and they have been aligned (as best as is possible). Just go to the main menu and go to the panoramas page, and click on one of the thumbnails. This will display the photo comparison program which lets you fade from one year to another. You can also select different locations.

The red lines on the left and right edges mark North. I will make this more explicit in the descriptive text when I get back.

Not much other news: I've taken lots of photos for PhotoSynth, but it isn't practical to do process these until we're back (Microsoft in their wisdom wrote PhotoSynth so that it only processes when online).  Oh, and another big rock/lava fall on the north side of Arenal visible (and audible) from the cabins. Two in one week. Activity does seem to be swinging around to the north side.

Our first panoramas are up!

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We re-shot two of the panoramas this morning, and I've been working on data processing. Although there hasn't been any careful alignment with 2008's photos yet, we have two of of the 2009 panoramic photos up:

(the new panoramic photo view requires the Silverlight 2 plugin installing)

As you can see, the growth around Bird Point C is quite amazing. Look at the teak saplings in the distance, and the cabins (in 2008).

I should have all of the panoramic photos processed by tomorrow, and then I'll start aligning them. First impressions are that alignment is not as critical as I was fearing. (I am also starting to experiment with PhotoSynth - more news when I have something to show)

In other news, this has been quite an adventurous day but everyone else has covered that. The main message is that parents should not be worried!

(oh and there was a small explosion, well really a burp, from Arenal - unusual in that I was actually watching and saw it before the sound reached us)
Yes we arrived here safe and sound. I'm sure everyone else has filled you in on what we've been up to. It is amazing how much has grown in the last 12 months. It should show up well in the panoramic photos. We have a smaller group this year but we've been making lots of progress. Natalia and myself have completed most of the panoramic photos although they need some formatting. I have also just updated the map with Nick's ant trap locations (marked with insect icons - I need to update the key when I get back), and a modified location for one bird point which we had to move due to fence/path changes.

The weather has been co-operative. Lots of rain but it is typical rainy season weather, arriving mid-afternoon. So we have some clear mornings, like the photo below of Arenal that I took this morning from our cabin.

It is quite common for strong winds across a prominent peak (eg. a volcano) to form a "cap" cloud or lenticular cloud (similar but above it), as the air is forced up, condenses, and then sinks again. Here we have the 'cap', but the hot steam from Crater D is being carried down the west (right) side of the volcano in the downdraft. Then when the downdraft stops, buoyancy takes over and we get the convection cloud on the right. And this has two lenticular clouds of its own above it!  A photograph for the meteorologists, I think!


arenal_lenticular_downwind.jpg

We have also seen land slides (?active lava?) on the north east side for the first time - this was yesterday lunchtime in the grey area to the right. A large amount of rock fell and it almost reached the vegetation. This has become more common in the past year and many people think activity will switch to this side soon.

Darwin is Right!

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The entire Costa Rican experience is so amazing so far. It is impossible to summarize it all in one blog entry. Even though we either had no sleep or little sleep on Sunday, we all got here safe, encountering little to no problems.When we got here we travelled around a little visiting a few places - The Fortuna Park and the surrounding towns. We travelled through Monterey and arrived at Leaves and Lizards at about 6.00 pm, three of us having no idea the adventure that awaited us here. We all settled in comfortably and took an early night, even though sleeping was hard to do since we are all so excited. On Monday, every one got a lot of rough work and preparation for the rest of the week. It was amazing. Geovanni, Dr. Brown, and I discovered 56 species of birds and many of them were new from last year. On Monday as well, we hiked up Mount Arenal, the active volcanic mountain in the pouring rain. It was a refreshing experience. When we came down the Mountain, we watched it erupted. Mount Arenal is so magnificent. Tuesday was equally exciting. I discovered a Green Breasted Mango, a species of Hummingbird for my hummingbird study. Even though sitting in the scorching heat with many ants and bugs and dogs, it was well worth the experience. I learned a lot about the nesting habits of the Mango. One thing that was especially interesting about the Mango is not only it's territorial behavior when it is nesting but also the fact that the male Mango is the only parent that was observed so far incubating the young. We've seen so many new bird species from last year, including the Breasted Mango as well as nine plus species of hummingbirds and a few that can't come to mind right now. The rest of the experience is very refreshing and thrilling. Hiking through forests and encountering bugs, possible snakes and the RAINFALL is all an extremely wonderful experience. My Darwin experience - standing beneath this fully shaded tree and still getting wet from the rainfall. It is really intense. The Costa Rican food is amazing and some of the best I have had in a few months. Dr. Brown and Mr. Marsden have helped us so much and Steven and Debbie have been so hospitable to us as well as Madesia. Gotto go. Until next time, hasta la vista.

Volcan Arenal Status

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This time next week, we'll probably be hiking across an old lava flow in the shadow (and earshot) of Arenal, so time to check the status:

Here is last week's entry from the Smithsonian's volcano pages:


6 May-12 May 2009

OVSICORI-UNA reported that during April activity originating from Arenal's Crater C consisted of gas emissions, sporadic Strombolian eruptions, and occasional avalanches that traveled down the SW, S, and N flanks. Acid rain and small amounts of ejected pyroclastic material affected the NE and SE flanks. Small avalanches of volcanic material traveled down several ravines. Crater D showed only fumarolic activity.

Major Arenal Pyroclastic Flow

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Latest report from the Smithsonian / OVSICORA-UNA:

4 June-10 June 2008

OVSICORI-UNA reported that an incandescent avalanche descended Arenal's SW flank on 6 June producing an 800-m-long scar and depositing a wide debris fan at the base of the volcano. A plume of dust, ash, and gas drifted W and NW, depositing fine ash in a small area downwind. The plume panicked tourists and park rangers 2 km away to the W. The park was immediately closed for the day and the tourists were evacuated. According to a news article, another incandescent avalanche descended the SW flank on 10 June and generated an ash plume. Authorities evacuated people in the area.

Sources: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA), Nacion




Lava Flow!

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The UD Field Ecology students after walking the 1992 lava flow from Arenal.  Front row from left:  Katheryn Miller, Katherine Biernat, Noah Jouett, Lorea Ormazabal, Johanna Weston, Samantha Behrent.  Back row:  Adaire Chatry, Mary Boyum, Richard Marsden, Christopher Gurguis, Adriane Smith.

group_volcano.jpg





Volcan Arenal, by Jorge Barquero Hernandez (Lihssa San Jose, 2006) is the last of the volcano books that I shall be reviewing here. It is also the shortest at 50 pages, but contains the best photographs of Arenal of any of the books reviewed in this blog. It is available directly from the Arenal Volcano National Park (Parque Nacional Volcan Arenal).

The text is bilingual English/Spanish and documents Arenal's activity from 1968 to date.
The only shortcoming is that I would have preferred more text, but the photographs more than make up for this. Photographs include a rare pre-1968 photograph, as well as good coverage of the aftermath of the 1968 Vulcanian eruption, and various activity over the past 40 years. There are lots of good night-time photographs of incandescent lava and Strombolian activity. Also included are some excellent time-lapse stills of pyroclastic flows. These are amongst the best photographs that I've seen for portraying the speed and unpredictability of pyroclastic activity.

Volcanoes, by Peter Francis and Clive Oppenheimer (2nd Edition, Oxford University Press 2004) is probably the best volcano book currently in print. The late Peter Francis wrote the original first edition, which quickly became a classic when it was published in 1993. Clive Oppenheimer has done an admirable job of updating the text and covering more recent eruptions such as Soufriere Hills (Montserrat).

The target audience is definitely an educated audience, but a knowledge of geology is not necessary. Volcanology and igneous petrology both suffer from a lot of jargon, but Francis & Oppenheimer do a good job of concentrating on what is important. There are even some witticisms regarding the more obscure (but loudly argued) areas!

Coverage of Arenal is limited to a few sentences in the discussion of Vulcanian eruptions, and whether the bombs erupted in 1968 really were supersonic. Better coverage and photographs are provided for neighboring Poas which is noted for its phreatic eruptions. Despite these limitations for our study area, this book is strongly recommended for those who want a comprehensive and readable book about modern volcanology.

Active Lavas: Monitoring and Modelling, Edited by Christopher R.J. Kilburn & Giuseppe Luoungo; UCL Press 1993
This out of print book concerns the monitoring and modeling of lava flows with the intention of improving future monitoring and the protection of civilian populations.

As such it is is probably a bit specialized for our needs. However, of interest to us is Chapter 2, The blocky andesitic lava flows of Arenal volcano, Costa Rica (pp 25-72). This takes advantage of the almost-constant effusion of Arenal's lava flows over the preceding 15-20 years to study lava flows on all scales from individual flows up to an entire volcano.

The result is a very good description of the morphology and dynamics of Arenal's lava flows. Of particular note are the field observations of which could be easily mis-interpreted by a field geologist studying an ancient lava field. For example, striations of lava flow levees could be mis-interpreted as fault slickensides. Selective erosion, truncated lava flows, and accretionary levees are also analyzed.

There are some useful lava flow descriptions which I shall be using in my volcano presentation, but otherwise this book is for a technical (field geologist) audience.


The The Volcano Adventure Guide, by Rosaly Lopes (Cambridge University Press 2005) is intended for volcano visitors who want more than what the usual tourist guides can provide. As well as an introductory section on volcanism, chapters cover safety and planning a volcano trip. Most of the book covers a range of volcanoes that are (generally) readily accessible. Volcanoes are chosen according to notoriety, things to see (eg. an eruption in progress), and accessibility.

Regions covered are: Hawai'i; Continental USA; Italy; Greece; Iceland; Costa Rica; and the West Indies.

Volcano coverage includes history, maps, places to visit, and guidelines for repose (or in the case of Arenal, "bad weather"). Lopes also adds personal accounts which range from the human (1 million people living on the slopes of Vesuvius) through to her own potentially hazardous experience on Arenal.

The technical level is aimed at the interested lay reader. Gives a good sound coverage - much better than the average tourist guide, but does not get into technical details that might swamp most readers.

This is an excellent book for someone considering a visit to a volcano or two. It can be used to choose volcanoes to visit, and also to plan your actual visit. Of course volcanoes have a tendency to change, but the book should give you enough information so that you can find out the latest status before your planned visit.

Chaiten Erupts

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The volcano of Chaiten in Chile abruptly woke up on 2nd May. I have yet to see any official analysis, but reports and photographs suggest a Plinian eruption is in progress. Some impressive photos can be found at Times Online and other newspaper sites. The Smithsonian pages for Chaiten have yet to be updated with news, but include some useful background.
Last eruption was about 9000 years ago. Caldera with rhyolite lava dome - famed as a source of obsidian in archaeological circles.

Chaiten is a long way from Costa Rica but both are home to subduction zone volcanism. Also, Plinian eruptions are relatively rare - there have probably been about half a dozen worldwide during my lifetime - so this is of note.

Regular reports of activity at Arenal are produced by the Observatorio Vulcanologico y Sismologico de Costa Rica - Universidad Nacional (OVSICORI-UNA). English language translations are usually published by the Smithsonian Global Volcanism Program roughly every month. The latest report is typical of recent activity from the past few months:


16 April-22 April 2008

In March, activity originating from Arenal's Crater C consisted of gas emissions, sporadic Strombolian eruptions, and occasional avalanches from lava-flow fronts that traveled down the SW flanks. Volcanic activity was at relatively low levels and few eruptions occurred. Acid rain and small amounts of ejected pyroclastic material affected the NE and SE flanks. Eruptions produced ash plumes that rose about 2.2 km (7,100 ft) asl. Small avalanches of volcanic material traveled down several ravines. Crater D showed only fumarolic activity.



Volcan Arenal

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Volcan Arenal is only a few miles away, and the study area has excellent views of the volcano when it is not shrouded in clouds.

Arenal is a active basalt-andesite stratovolcano. It is the youngest volcano in Costa Rica and has been erupting continuously since 1968. This is very unusual for an andesitic subduction zone volcano. This long lasting eruption and relatively accessible location, make Arenal one of the top locations in the world if you wish to see an active eruption in progress.

The 1968 eruption started with a Vulcanian explosion, but is now primarily Strombolian with lava flows and occasional pyroclastic flows.

Arenal is showing signs of reduced activity but continues to be very dangerous and has killed people in recent years. Do NOT climb the cone, do NOT enter closed areas, and take heed of ALL warning signs.

arenal_Jan01.jpg