This post grew out of the GVP summary for mid-February as Ambrym’s current eruption was winding down. One thing kind of led to another …..
Ambrym Island hosts an active volcano with a pair of active vents, Mount Marum and Benbow. They occupy a 12 km diameter caldera created during a VEI 6 eruption around 50 AD. Both active vents host lava lakes.
Activity around Feb 21 was associated with what was described as a minor eruption from a new vent inside the caldera. Over the following couple weeks, activity decreased and the Alert Level is now listed as a 2 out of 5. Hazardous areas are defined as areas near the new vent and downwind areas prone to ashfall. http://www.geohazards.gov.vu/
The last eruption started in 2009 and is listed as ongoing.
Like Hawaii, Ambrym gets a significant amount of rain, which is heavier on the windward side and lighter on the leeward side. Average difference between the two sides is about half. Average rainfall is around 210 cm yearly. Given the soft nature of what has built the island, this leads to significant erosion. It also has the effect of making escape from rising water down the steep slopes of the cut ravines problematic as the soil is soft and difficult to grab hold or climb up.
Ambrym Island is part of the nation of Vanuatu, a collection of volcanic islands situated equidistant north of New Zealand and east of Australia. The island is just under 680 km2 and the volcano is some 1,300m high. Total population of the island is around 7,300 as of 2009.
Volcanic activity is driven by the subduction of the Australian Plate under the Pacific Plate. Basic movement by the Australian Plate is easterly. Basic movement of the relevant portion of the Pacific Plate is WNW. The region is tectonically complex with a spreading center in the Pacific Plate to the east of Vanuatu. The subduction trench to the west of Vanuatu is called the Vanuatu or New Hebrides Trench. The Tonga Trench sits east of both Vanuatu and the spreading center in the Pacific Plate.
One of the things that makes New Zealand so geologically volatile is that the Australian Plate is subducting under the Pacific Plate to the south of it and the Pacific Plate is subducting under the Australian Plate to the north of it. Crossover of the subduction zones is roughly in the center of the country. The Taupo Volcanic Zone sits north of this crossover area.
Vanuatu is similarly complex, with the triangular area bounded by the subduction trench to the west and the inactive trench segment southeast of it sometimes being referred to as the Fiji Plate. There is a discontinuity bounding the north of the area that may or may not be defined as a plate boundary. Because of the subduction to the west of Vanuatu, it is a very geologically active nation, with a large number of large caliber earthquakes.
Ambrym Volcano is primarily a basaltic volcano with andesitic output. The edifice constructed is a combination of lava flows and pyroclastic deposits, with the pyroclastic debris predominating. It is one of the most active volcanoes in the world. There is enough effusive output to support the lava lakes in the two craters. However the majority of eruptions is explosive, usually from a central vent, and also produces lava flows. Unlike Hawaii where lava flows predominate, the majority of the stuff that has built Ambrym (and its neighbors) is ash and pyroclastic materials, making the island itself very prone to invasive water from the surrounding ocean, which in turn lead to more explosive style of eruptions. http://www.vanuatu.travel/index.php/en/things-to-do/volcanoes/112-ambrym-volcano
The caldera is referred to as the ash plain, as it is mostly covered with pyroclastic debris.
There are rifts on the island which feed magma to the surface. This has led to phreatomagmatic eruptions and craters on either end of the island where the magma meets with seawater near the surface. Craters are typically 1000 m in diameter with rims some 100 m high. The most recent eruptions of this nature on Ambrym were 1894, 1913, 1937 and 1954. Similar features show up on other Vanuatu islands.
At least one paper describes the central caldera as a subsidence structure much like the calderas of the Hawaiian and Galapagos Islands. There is some dispute over that description given the VEI 6 eruption some 1900 years ago.
Geologic evolution of the island is poorly understood.
Ambrym is and will continue to be an active and dangerous volcano, capable of very large Plinian eruptions. For a basaltic system, it produces a significant amount of pyroclastic output. Local tectonics are complex and active. It is a most interesting part of the world.
Note: I am no expert; merely an amateur who is interested in how things work and why. Corrections and suggestions are always welcome and encouraged.
A Nobel Prize for Volcanology – Dr. Stephen Sparks
In January, Dr. Stephen Sparks was awarded the 2015 Vetlesen Prize. This may not be “news” anymore, but as we read so much of Dr. Spark’s work we thought it is something important to mention on a volcano blog:
(OSU Volcano World) A Nobel Prize for Volcanology
Volcanology has a new Nobel Prize winner! Dr. Stephen Sparks has received the 2015 Vetlesen Prize, awarded by the G. Unger Vetlese Foundation and Lamont-Doherty Earth Observatory. The Vetlesen Prize is considered to be the Nobel Prize in earth sciences, awarded to individuals who have made significant scientific achievements in establishing a clearer understanding of the Earth and its workings. Currently located in the University of Bristol, UK, Dr. Sparks received this great honor because of his work in improving our understanding of global volcanic hazards. His work on Montserrat’s Soufrière Hills volcano has helped goverments asses danger from volcanic eruptions and improve their evacuation and hazard response. Internationally, he has helped with the improvement of volcanic risk assesment, and has been awarded several honors because of his work.
For more about Dr. Sparks and his work, read this article:
Geologist Who Modernized Volcanology Wins the 2015 Vetlesen Prize
This video is well worth watching!
Hi agimarc, thank you for this overview of Anbrym’s activity, what an interesting corner of the world! Unfortunately, all the online webcams, seismograms and the alert level map have stopped updating since that last cyclone disaster ten days ago, hopefully the equipment has not been destroyed.
Thanks, agimarc, great post on a fascinatingly odd volcano. This might be of interest:
Click to access 39468.pdf
MD – Excellent paper. Many thanks. Cheers –
I love odd volcanoes.
Ambrym is a fascinating island, here are a couple of my photo’s from last July
Marum crater (there is also a small side crater that has a small lava lake making 3 in total)
Both craters glowing from their lava lakes
Thank you Doug, that are great photos! It is hard to imagine what it is like when a volcano is “always on”. Did you have a guide there, or did you get a chance to talk to the people fron the observatory?
Outstanding photos, Doug. Many thanks. Cheers –
It is sure an interesting article on a remote volcano. I hope that the population there did not suffer overmuch of the cyclone.
thanks 67Doug for the additionnal pictures.
The slopes of the craters seem well weathered.
They are because they are soft. Much pyroclastic output and some lava as compared with Hawaii’s much lava and little pyroclastic output. Soft stuff weathers quickly. Kind of makes me wonder why there are islands out there. Cheers –
From geonet’s (New Zealand) latest Volcanic Alert Bulletin NGA-2015/01 – Ngauruhoe Volcano
Seismic activity around Ngauruhoe has increased above the typical background level, indicating minor volcanic unrest. Consequently GNS Science has raised the Volcanic Alert Level to level 1 (minor volcanic unrest) from 0 (no volcanic unrest). During the last two to three weeks there has been an increase in the number and magnitude of earthquakes being recorded by the GeoNet seismographs around Mount Ngauruhoe. Initial analysis indicates these earthquakes are shallow, occurring at depths of less than about 5 km. The last significant eruption at Ngauruhoe was in 1975.
Can someone describe how to pronounce Ngauruhoe?
Where’s Bruce Stout when you need him?
Now roo hoy
LikeLiked by 1 person
Oo noo broon coo
What’s that in plain English?
Annunciation exercise, How Now Brown Cow, supposed to correct people dropping consonants from words in dialect, the way to pronounce Now roo hoy just reminded me of it.
On topic, Iceland is going to tear itself apart at a possible time in the future and some volcanoes will explode a bit, or even more than a bit, probably quite a lot in point of fact and it is interesting to see the continued jiggling about going on along the whole MAR under Iceland. Just me or was it a lot quieter elsewhere when Bardy was pushing it’s stuff out?
My take on Iceland is a bit different than that of most other people here arounds. I don’t know about the experts, but I am not one anyways, so I can just have an opinion… Iceland is not tearing apart but is growing very quietly from within, and has been doing so from its very beginnings. Naturally, with the magma welling up, eruptions occur every now and then. Depending on the conditions, whether or not there is a lot of water involved from the surface, and the amount of magma playing a role, they can be more or less energetic, but never as big as some of the volcanoes in the subduction zones are capable of.
There is a lot going on tectonically in Iceland but the volcanic activity is far less than in other regions of the world, and that makes it sort of boring – to me – to look at Iceland for a longer time. It moves, it heaves, it bulges, it cracks, it coughs – and nothing comes of it… at least very rarely compared with other places. That doesn’t mean I did not appreciate the Nornahraun eruption, it was great as long as it lasted! 🙂
Wow, Colima is having a good time right now!
And so is Villarrica!
Info from the last 6 hours in various Chilean newspapers:
During the afternoon of Tuesday, a flyover on Villarrica volcano by SERNAGEOMIN confirmed that lava into the massif is close to the crater surface again. Although in the last two days emissions of ash and gases had decreased, at nights a bright glow was observed in the crater area. Accompanied by a continuous seismic tremor of moderate energy which has remained constant values for most of the day with a slight upward trend.
Currently, restriction zone on the volcano is fixed at five kilometer radius around the crater but could be increased to 10 km if necessary, also OVDAS included Challupén river estuary into the danger zone.
The alert level is still at orange. A probable scenario would be similar to what happened last March 3 at the first eruption this year.
Images courtesy of SEBASTIAN ESCOBAR/AFP/Getty Images (1st) and SERNAGEOMIN (2nd), showing the glow of crater area at night, and a thermal camera image, suggesting a magmatic body close to the surface.
Do we have someone ornithologically inclined here? I just captured these birds on the three Shiveluch webcams, it would be interesting to know what they are. Perhaps one can tell from their appearance of flight? Click on the image for large view.
They might be Steller Eagles
That would be my best guess too, although harder to tell because of the lighting not showing colour and no clear silhouette of the head. The wingtips and general body shape and tail look about right though.
Wow, they are among the biggest birds of prey in the world! Although, they do have a lot of white in their plumage. I would think that would be visible in the images, even against the sky… well, not sure. Thanks a lot for your replies!
new pics of nishinoshima
Now that the initial phase of the Bárðarbunga/Holuhraun episode is over, we can look back and say, how would it have been had it been subglacial? 1.4 km3! How much of the Vatnajökull would have survived an eruption of that size? Would the phreatics and *tremendous* jokullhauping have destabilized sections of the glacier beyond the near vicinity? If the lava had erupted where the dyke doglegs left (which is not a farfetched idea), how would things look now? We got lucky…
It isn’t over yet
Heads-up for Sakurajima everyone.
Average 450 eruptions a year. So far in 2015, over 300 eruptions.
31 eruptions on March 27th alone. I’ve been watching the webcam:
Deformation/swelling/inflation has been reported.
This is potentially shaping up to be something biggish. Raw data (in Japanese) from JMA: http://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/volinfo/gensho.html
(This report from my own observations and from a contact in Japan)
The inflation that was occurring a few years ago was centered on Wakamiku crater, in the northeast of the Aira caldera, not under Sakurajima. While Sakurajima may be the outlet for now, I suspect that eventually we will end up seeing the formation of a new somma volcano next to Kirishima. Those could be some interesting times.
Howdy Mike – With your connections and expertise, any chance of a post on Sakurajima? Cheers –
New post “Activity increases at Semisopochnoi” is up. Things are percolating nicely out there. Might be a reprise of last year’s earthquake swarm. Might be something larger. Webicorders are cranking up nicely. Cheers –
Pingback: Volcanoes of Samoa – Part 1 of 2 |