After the excitement surrounding the eruption of Nabro yesterday it seems that activity has died down. At the Volcanism Blog, photos show the current situation nicely. It may well be that the eruption has turned more effusive in nature, however we won't fully know until information is received from around the volcano - information is a little cloudy at the moment.

Puyehue-Cordón Caulle is still erupting but is less active than when it first erupted. Below is the latest webcam image from sernageomin.

Elsewhere at the Dieng Volcanic Complex the current period of increased activity is continuing with the alert remaining at Level 3 for the second week running. Seismicity and gas emissions (specifically CO2) remain at elevated levels. For full info see the Global Volcanism Program weekly updates. 

Will be posting later today on Galeras, Colombia the next volcano in the decade volcano series.

Sources
The Volcanism Blog
Global Volcanism Program

It appears that I was a bit premature earlier in assuming, as reports at the time had suggested, that the eruption was from Dubbi! As new information has come to light (discussed in the eruptions blog and the volcanism blog) it appears that the eruption has orignated from the Nabro volcano. A subtle reminder to us all that volcanoes and volcanology can be quite unpredictable! A little about Nabro is posted below.

Nabro, which is located in the Danakil depression is a mysterious volcano located at the South-Easterly end of the Danakil alps. It is the highest peak of the Nabro Volcanic Complex at ~2218 m. The Nabro volcanic complex is a roughly NNE to SSW trending system with Dubbi at the most NNE point, Nabro in the centre and Bara Ale at the most SSW point. The length of the complex is roughly 110 km. At the summit are two calderas 5  and 8 km wide. Also present in the area around Nabro are lava domes, evidence of lava flows and ignimbrites. The lava flows are generally basaltic in nature whilst the lava domes and ignimbrites are distinctly rhyolitic in nature, there are also some obsidian flows in the area. It seems that the early evolution of Nabro was dominated by more evolved magmas (rhyolitic) and ignimbrite forming eruptions whilst later on in life activity became more effusive in nature. (Wiart and Oppenheimer, 2005)

I have kept my previous post on Dubbi active and is available here, it still provides a good overview of Dubbi volcano and volcanism in the area.

Sources
Wiart and Oppenheimer, 2005. Large magnitude silicic volcanism in north Afar: The Nabro Volcanic Range and Ma'alalta volcano. Bulletin of Volcanology  
Global Volcanism Program

NEWER UPDATE AVAILABLE: It seems I was premature in assuming the eruption was from Dubbi. The eruption is now believed to have originated from Nabro. I have left this post here as it is still an interesting overview of Dubbi and volcanism in the area.

An eruption of the Dubbi volcano, which is located in Eritrea, has started after a series of strong earthquakes were detected and has spread an ash cloud ~1000 km from the summit. The eruption is believed to have started at  21:00 UTC on the 12th June. For full information on the eruption visit the Volcanism Blog for more information. Here I am going to give a brief overview of Dubbi Volcano, its past eruptions and why volcanism is seen here.

Dubbi is a stratovolcano at ~1625 m high. It has known several previous eruptions of which ones in 1400 and 1861 are confirmed. Further eruptions in 1863 and 1900 remain unconfirmed. When dubbi erupts it has produced both an explosive eruption at the source vent and lava flows which can be seen trending off towards the see in the photo on the right.  At the summit of Dubbi are a number of scoria cones according to John Seach. Dubbi generally produces effusive basaltic volcanism after a more explosive stage involving rhyolitic products - this was the case in 1861.

In 1861 the eruption began in an explosive ash producing manner, with pumice and highly mobile pyroclastic flows produced which stretched to ~25 km from the volcano. After this stage, the eruption became more effusive with a series of scoria cones produced and lava flows which stretched up to 22 km from the source area were also quite thick ~20 m in most places. Overall this eruption produced ~3.5 km3 of magma, meaning that it is the largest eruption of an African volcano in historical times.Please read Wiart and Oppenhiemer for more detailed info on this eruption.

Geologically it's position is extrememly interesting, Dubbi is located at the Afar triple junction, where the Arabian, Somalian and African plate are interacting. There is also a mantle plume (or hot spot) in the Afar triangle area. Dubbi is in the southern part of the Afar trianle and is part of the East African Great Rift Valley. The volcanism at Dubbi is probably associated with the spreading of the plates at the centre of the red sea. The Afar triangle is more famous for the active lava lakes of the Erta Ale Volcano.

Sources
John Seach
Wiart and Oppenheimer, 2000. Largest known historical eruption in Africa: Dubbi volcano, Eritrea, 1861  Geology 28, p. 291-294

Today is the turn of Mt. Etna. Having recently visited Etna this post may be a little longer than the others so I apologize! A recent Daily Volcano Quote by the Volcanism Blog, available here summarises Etna extremely well! I have previously posted on etna in the following posts on lava stalactites, xenoliths, Rifugio Sapienza and a view of the composite cone. You can view all of these by clicking on the category for Etna along my sidebar.

Etna is a stratovolcano which has been built onto an older shield volcano. The entire volcanic complex is ~ 500,000 years old. The reason for its location is complex and there are many theories but it is generally belived that it's location is down to the extension of the crust because of the reversal of the Ionian slab.

The first edifice started forming ~180,000 years ago and is built up of a large number of pyroclastics and lavas. The last 14,000 years of edifice formation is referred to as the Recent Mongibello, which is also the name of the current summit crater (Mongibello).

Etna is characterised by smaller explosive eruptions such as Hawaiian and Strombolian activity accompanied by lava flows which occur both from the summit craters and eccentrically (on the flanks of the volcano). More rarely Etna has seen basaltic plinian eruptions in 122 B.C. and 44 B.C. Baslatic plinian eruptions are rare themselves.The lavas which are generated at Etna tend to be either ʻaʻā  or pahoehoe in nature. Pahoehoe is the lava which is commonly seen on Hawaii, it is runny and less viscous. ʻAʻā is more viscous and is generally characterised by a more blocky morphology. Etna experiences regular outbursts of activity the most recent occuring within recent months.

Tomorrow is the turn of Galeras, Colombia. The following are a couple of interesting articles on Etna. For more general information see the global volcanism program. Thanks for reading!

Gillot, P.Y et al. 1994. The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanol. 5, pp. 81-87

Guest, J.E et al. 1984. The valle del bove, Mount Etna: Its origin and relation to the stratigraphy and structure of the volcano. Journal of Volcanology and Geothermal Research 21 (1-2), pp. 1-23

Monaco, C et al. 2005. Tectonic control on the eruptive dynamics at Mt. Etna Volcano (Sicily) during the 2001 and 2002-2003 eruptions. Journal of Volcanology and Geothermal Research 144, pp. 211-233

I have recieved an email asking me to go into a couple of things which I mentioned in this post.

The first question asked how water causes lightning in eruption columns, and whether this is similar to meteorologically generated lightning in thunder storms.
The boiling of water in plumes and consequent rapid disruption of water molecules causes them to shear (or break-apart) this can create a charge which is more positive in larger molecules and more negative in smaller molecules. In eruptions including seawater, the salt included becomes negatively charged. This process discussed is different to the thunderstorm charging mechanisms. However a paper by Williams and McNutt (2005) does propose that the thunderstorm charging mechanism may occur in volcanic plumes (particularly at volcanoes located at high atltitudes with ice). To my knowledge thunderstorm charging is to do with collision of particles and how fast these
 
It should be stressed that there is not one 'correct' reason for lightning charging in eruptions and it could well vary from plume to plume dependent on a variety of factors!

The second question asked how lightning in a volcanic plume is used to infer height.
There is an excellent overview of this located here. The Met Office (UK) has used this during the eruptions of Eyjafjallajökull and Grimsvotn. Research has found that the number of lightning strikes per hour (or the amount of activity) increases proportionally with plume height. Therefore a rough plume height can be inferred. 

I hope this helps!

Colima is the most active volcano in Mexico having erupted more than 40 times since the mid 1500s and in my opinion is among the most beautiful on the decade volcano list.

The Colima Volcanic Complex consists of three peaks. The currently active peak, named Volcan de Colima (the decade volcano) which stands at ~3850 m and is also known as Volcano de Fuego. The older but taller Nevado de Colima (~4320 m) sits to the North of its younger counterpart. The eroded Cátaro peak (~2500 m) which lies further to the North still. Colima is located in the Trans-Mexican Volcanic Belt and is the result of the subduction of the Cocos and Rivera tectonic plates beneath the North American counterpart.

The current eruptive period at Colima has been ongoing since 1997 with the main type of explosion which occurs here Vulcanian in origin. Vulcanian eruptions are generally described as short lived bursts which produce an ash/steam column which can range in height between hundreds of metres or generally to ~10 km. Effusive activity also occurs at Colima with lava flows occuring commonly throughout its history. Generally the eruptions are small in scale however larger eruptions (up to VEI 4) have occurred in the past which have destroyed the summit area
 
Colima is currently monitored by the Colima Volcano Observatory. For a panorma of the observatory visit this link. The website of the Observatory is available here, where you can find webcams, photos and more detailed information of the volcano. Due to it's location and easy access Colima has become one of the most studied volcanoes and this is in part due to the excellent management and work done at and by the University of Colima.

Please feel free to comment on this or any of my posts, I am open to suggestions and would love to have a little interaction with readers. 

As promised I am starting my posts on the decade volcanoes. Today is the turn of Avachinsky-Koryaksky. 

Despite being listed as one volcano, they are actually separate from each other. Avachinsky and Koryaksky are both part of the Avachinskaya volcanic group which is a group of stratovolcanoes which are orientated in a NW-SE direction. The other prominent volcano in this range is Kozhel. These volcanoes are the result of the Pacific plate subducting beneath the North American plate at a rate of ~ 78 mm a year. Due to the climate in the area and the amount of ice and snow on the volcanoes the main hazard posed from Avachinsky and Koryaksy is by lahars with Pyroclastic Density Currents a close second.

The town present in the foreground of the photos below is Petropavlovsk.
 
Avachinsky is a stratovolcano which stands at ~2741 m high. The last eruption of this volcano was a tiny eruption in 2001 with another small eruption in 1991.  An event in 1945 was much larger and was rated at VEI 4. The eruptions produced by Avachinsky are generally smaller in scale at ~VEI 2. Avachinsky also houses an active crater with regular degassing and fumarolic episodes.

Koryaksky is the taller of the volcanoes in the range, standing at ~3456 m. Overall it is less active than Avachinsky and less is known about its past eruptions. The last eruption of Koryaksy occured in 2008/2009 and was rated at VEI 2, in general this eruption was characterised by steaming with small amounts of ash within the column.  

During my studies I came across the decade volcanoes. Now, I hadn't heard of these before and was intrigued to learn which ones they are and the purpose that they serve as being named 'Decade Volcanoes'.

They were set up by the International Association of Volcanology and Chemistry of the Earth's Interior to promote research on these volcanoes. They were chosen for a number of reasons including their history of large explosive eruptions, their proximity to populations and their effect on people. The overall aim was to increase public awareness and reduce the volcanic hazard posed by these volcanoes. 

So here they are...

Avachinsky-Koryaksky, Kamchatka
Colima, Mexico
Mt. Etna, Italy
Galeras, Colombia
Mauna Loa, Hawaii
Merapi, Indonesia
Niragongo, DR Congo
Mt. Rainier, Washington state (USA)
Sakurajima, Japan
Santa Maria/Santiaguito, Guatemala
Santorini, Greece
Taal, Philippines
Teide, Canary Islands, Spain
Ulawun, Papua New Guinea
Unzen, Japan
Vesuvius, Italy

Over the next few months I will write a bit about each of these volcanoes, starting with Avachinsky-Koryaksky, Kamchatka.

We have all seen the spectacular photos of eruption columns and lightning but why does it happen?

The majority of study on lightning in eruption plumes has been done on silicate rich plumes. These are the dark grey plumes you see in more plinian type eruptions (such as pinatubo), phreatomagmatic and some vulcanian eruptions. It is within these columns that lightning is more common.  

In general within these columns the larger particles at the base of the plume with smaller at the top. Within the column the overall charge is moe positive at the top and more negative at the base. This creates what is termed a dipole and consequently lightning occurs. However there are other mechanisms based on the type of eruption, the content of the eruption and the location (altitude). 

There are two main ways which plumes are thought to become charged; these are during the fragmentation process (often termed fractoemision) and the boiling of water (often a common volatile in eruptions, but also an addition during phreatomagmatic eruptions). Fractoemission occurs during the fracturing of a material (in volcanic cases - magma) this then causes a the release of electrically charged atoms, ions and radiation in different circumstances. Fractoemission is thought to be the dominant charging process.

So why is volcanic lightning important to study? Firstly, it can be used to infer plume height. This was done during the recent eruption of Grimsvotn in combination with the UK met office. It is important on extraterrestrial bodies (other planets) and may have played a role in the origin of life on our own planet Earth. Volcanic lightning also represents a hazard to people and has killed people in the past during eruptions of Paricutin and Rabaul. 

This is just a brief, and simplified overview, for those of you with access to journals and want a more detailed explanation, the following are articles on lighting in volcanic plumes.

James et al. 2008. Electrical Charging of Volcanic Plumes. Space Science Reviews 137, pp. 399-418

Mather and Harrison, 2006. Electrification of Volcanic Plumes. Surv Geophys 27, pp. 387-432

McNutt and Williams, 2010. Volcanic lightning: global observations and constraints on source mechanisms. Bulletin of Volcanology 72, pp. 1153-1167

I have posted three of my favourites below. The last photo of Krakatau just goes to show that it doesn't have to be a violent eruption to produce lightning! My personal favourite though is the one of Chaitén - very atmospheric. 

Puyehue-Cordón Caulle continues to erupt but with diminshed activity, there are detailed reports in the Eruptions blog by Erik Klemmeti and The Volcanism blog.

I have posted a couple of the more spectacular photos of the eruption column, I will be posting tomorrow about what causes the volcanic lightning so often seen in eruption columns! It's something which is seen so frequently that I feel it should be explained!