The Santa Maria volcano awoke with a loud bang in the year 1902 with a large Plinian eruption that left a large crater in it's place. The eruption of 1902 billed as a possible VEI 6 eruption possibly killed as many as 5000 people.
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Photo: Lee Siebert. Santiaguito erupting beneath Santa Maria.
Now, however the activity is located at the Santiaguito Volcanic Dome Complex at the base of Santa Maria and within the crater created by the 1902 eruption. Eruptions at this location started in 1922 and have been continuing to the current day. This complex currently consists of four dacitic volcanic domes with only one that is currently active the Caliente Dome. Santiaguito is famous for its consistent one to two hour vulcanian events. Other activity which occurs are Pyroclastic Density Currents, Lahars and an occasional larger event than its usual vulcanisn bursts. The most recent of these larger events occurred in 2010 and created a large ash column with associated Pyroclastic Density Currents and crater collapsing. The Santa Maria/Santiaguito complex recieved its Decade Volcano status because of the large hazard it poses to the population in Guatemala and the lack of funds locally to monitor and study the volcano sufficiently.

For full details on Santiaguito and some interesting posts I thoroughly recommend the Magma Cum Laude blog.

I have posted a video below from youtube of a typical event at Sanitaguito, the video itself was taken from the slopes of Santa Maria.

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Galeras in Colombia is one of the most active in the country and has seen regular eruptions for the past 1 million years. With 7 eruptions since the turn of the century and one occuring in 2010 the activity hasn't stopped since. The 2010 activity caused the evacuation of 8000 people from its vicinity. A nice overview of the area is available here at the NASA Earth Observatory.
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From the GVP page for Galeras.
Galeras at ~4276 m high is a stratovolcano which towers over the town of Pasto and produces predominantly andesitic products. The reason for volcanism at this location is the subduction of the Nazca plate. A nice diagram of this is shown here. The summit of Galeras is complex as it has had a diverse and extremely interesting history, involving a couple of caldera forming events, one which occurred 500,000 years ago and the other around 100,000 years ago. In addition to these events a series of edifice collapse episodes have left a horseshoe shape at the summit.

Since the first historic eruption was recorded by the Spanish in the 16th century, the volcanism has been lightly explosive, producing ash clouds and pyroclatic flows in what can be described as vulcanian to sub-plinian events.

This volcano became infamous in 1993 when it sadly killed nine people (six of who were scientists) who were in the summit crater at the time of the eruption. Prior to this sad event, Galeras was designated a Decade Volcano in 1991.

Other Volcano News
Today is the 20th anniversary of the eruption of Pinatubo in 1991. Over at the Eruptions blog by Erik Klemmeti there is an excellent anniversary post, I reccomend you check it out!
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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.
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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.
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Photo on the left of an eruption in 2006. Photo on the right taken from the National Geographic and available at http://photography.nationalgeographic.com/photography/enlarge/mt-etna-eruption-photography.html.
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
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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.
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Volcan de Colima. Situated in the spectacular Nevado del Colima Park.
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.
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A vulcanian burst of Colima in 2007. Taken from the global volcanism program website.
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. 
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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.
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Avachinsky -From the Global Volcanism Program and taken by Oleg Volynets
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.  
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Koryasky - From the Global Volcanism Program and taken by Vera Ponomareva
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Avachinskaya Volcanic Group, from the Global Volcanism Program and taken by Vera Ponomareva. Koryasky is on the left, next on the right is Avachinsky and on the far right is Kozhel.
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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.
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