Saturday, August 7, 2010

ERUPTION TYPE OF VOLCANO INDONESIA

Escher (1952) classified volcano eruption type based on: viscosity, gas pressure and and dept of magma chamber, in to 7 types of volcano eruption:Hawai Type,Stromboli Type,Volcano Type,Perret / Plinian Type,Merapi Type,St.Vincent Type,and Pelle type.

Based on those types, Indonesia volcanoes at least have 4 types of eruption:Strombolian,Volcanian, Plinian, Merapi, and St.Vincent.While out of such classification base,another type of volcano eruption that Indonesia specifically has is Karangetang Eruption Type. Some Indonesia volcanoes also experienced Pheriatic Eruption which is used to be called as "minor eruption".

STROMBOLIAN TYPE:

It's name type originating from a volcano in Italy named Stromboli. Commonly low viscosity, so that release relatively low energy which is characterized by lava fountains, and used to be entailed by lava flow.Fragmented volcanic material erupted are sizing from volcanic ash to volcanic bomb, textured scoria ,eruption columns up to 100's m over crater ridge/summit.

Strambolian type of eruption is popular among volcano lovers for it's lava fountains. Spewing out fragmented volcanic material will then fall down back in to around summit  zone providing fantastic view of unique volcanic activity phenomenon. Some stayed on summit  zone while other flew down through volcanic flank. At night it provides red light which is visible from certain safe distance.Eruption is most commonly calm (Effusive) in style.

In Indonesia, Slamet volcano ( 2014 ) provides this kind of Eruption type. Some Other volcanoes tend for this eruption type : Raung volcano, Rinjani volcano, Anak Krakatau volcano, Sindoro volcano,and Tambora volcano. For Strombolian type of Tambora, it is worth to mention here that since 1847 a volcanic cone called Doro Afi Toi appeared at base caldera of Tambora and has been growing up, yet sometimes releasing Strombolian eruption until 1913. This little volcano was constructed by lava deposition which is now just blowing  fumarole fume occasionally covering its whole structure.

VULCANIAN TYPE:

Vulcanian eruptions are weak to moderate explosive eruptions, lasting seconds to minutes.Volcanic Ash columns can be up to 20 km in height, and lava blocks and bombs may be ejected from the vent.

Terms of eruption type volcano (vulcanian ) it self was firstly introduced by Giuseppe Mercalli, a person witnessed eruption of Vulcano, Italy , in 1888-1890. Eruption in thundering noisy,ejects volcanic ash and gas, also various size of volcanic rock fragments.

Those ejected fragments are commonly non juvenil sourcing from lava plug and volcanic fragments around crater.Thundering noisy is manifestation of gas release which being characteristic fiture of Vulcanian type. This type has medium gas pressure, also relatively less low viscosity. Based on it's explosive intensity, this type divided in two : Strong Vulcanian / strong explosive eruption and weak Vulcanian / weak explosive eruption. Some Samples: Kerinci volcano,Semeru volcano, Slamet volcano, Bromo volcano.

MERAPI TYPE:

Commonly has high viscosity,very shallow magmatic chamber,and low gas pressure.The type originating to Merapi volcano.During eruption phase, Merapi exhibits alternating volcanic activities of effusive and explosive characters and self destruction.

The effusive activities were characterized by the occurrence of lava flows, the development of lava dome, and the production of the “nuee ardente d’avalanche” called Merapi type.The explosive stage is frequently accompanied by the occurence of pyroclastic flows.This Merapi spesified type of eruption was absent on Merapi eruption 2010,made Merapi type transformed in to new another type ones

The eruption type then existed at Sinabung volcano on eruption at the end of year 2014. During this period,volcanic activity of Sinabung remains high. Lava appeared as a lava plug that was increasingly getting higher. When the plug enlarged, its equilibrium became unstable. In this condition, the very shallow magma suddenly pressed the lava plug, and produced lava avalanches in large volume. The avalanches flew down in
turbulent and produced pyroclastic density current or nuées ardentes.Such Sinabung eruption events are known as Merapi Type eruption.

PLINIAN TYPE:

Plinian type envolves very high gas presure that able to smash lava dome or any other lava plug, eruptions sustain for manutes to hours,eruption columns  of volcanic ash plume are as high as 20 to 35 km forming mushroom clouds,then cauliflower clouds wich are then may collapse to forrm as pyroclastic.Current sample for this was eruption kelud (2014),main eruption column as high as 20 km,by scale VEI 4.According to note of Global Volcanism Program, Plinian type eruption by scale 4 VEI saldom be occurred,average once each 10 years.

Sub-Plinian type:the eruption columns of plume up to 20 km high, and are relatively unsteady.Current sample for this was eruption Sangianapi(2014) where the eruption columns of plume rose as high as 15 to 20 km up to the sky, even the ash plume crossed to north-west coast Australia at Kimberley region. According to volcanology expert,Sub-Plinian eruption occurred due to high gas pressure smashing solid plug such us lava plug.This type used to left behind rest of crater large ventilator which is finally should be proved by field research on summit zone.

While Ultra - Plinian type ones :This very rare Ultra-Plinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions, it's eruption power is commonly able to collapsing partly structure of the volcano and transform it in to Caldera. According to the Smithsonian Institution's Volcanic Explosivity Index, a VEI of 6 to 8 is classified as "Ultra Plinian." They are defined by ash plumes over 25 km high and a volume of erupted material 10 km3 (2 cu mi) to 1,000 km3 (200 cu mi) in size. Eruptions in the "Ultra Plinian" category in historic volcano eruptions of Indonesia included: Tambora (1815), and Krakatoa (1883).

St.VINCENT ERUPTION TYPE:

Perhaps name of this type was originated to volcano St.Vincent.This type characterized by high viscosity, medium gas pressure, shallow in magmatic chamber.Popular sample of this eruption type in Indonesia was eruption of volcano Kelud (1919). According to history of eruption Kelud volcano as recorded at Data Dasar Gunung Api Indonesia 1979 ,there were 5160 victims of human being caused by eruption impact of Kelud on May 20, 1919.

KARANGETANG ERUPTION TYPE

Out of type classification proposed by Escher, in Indonesia there is another spesific type of eruption named Karangetang Type Eruption.This type originating to Karangetang volcano.The volcano it self stands on elevation 1,787 m height above sea level in the middle of the Celebes Sea, forming Siau Island in the North Sulawesi’s regency of Sitaro.Since 1976, Karanagetang volcano has often been exhibiting a firelight on its summit area.

Eruption of Karangetang formed glowing cloud occuring when the volume of lava flow is sufficiently large to form a bulge at the end of the flow of occured glowing cloud's spot.This spesific type of Karangetang eruption is named "Karangetang Eruption Type".The longest flow of the lava up to 16 km from the summit to the north,it was formed on year 1976 and popularlly named as  Lava Arengkambing .

THE "MINOR ERUPTION":

Another eruption existed in Indonesia was Phreatic eruption, non magmatic eruption,also commonly called as "minor eruption" in Indonesia.The eruption driven by the heat from magma interacting with water. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea. Phreatic eruptions pulverise surrounding rocks and can produce ash, but do not include new magma.The eruption normally take place in short of time and only affects around summit zone,but erupted ash can travel further according to actual wind direction.

Some volcanoes in Indonesia experienced Pheriatic eruptions, and Kerinci volcano was one of them. Based on history of Kerinci volcano eruption, Pheriatic eruptions occured at Kerinci volcano on years 1878 ( 11 Des), 1887?, 1908, 1936 ( 26 April and 30 August ),1938 ( between 19 January and 8 March ) as recorded at Data Dasar Gunung Api Indonesia.At Merapi volcano,on pasca eruption 2010 some Pheriatic eruptions also noted.

NOTES OF ERUPTION TYPE:

In fact, many volcanoes of Indonesia have multiple eruptions,let's say a sample such Slamet volcano possessing Strombolian and Vulcanian type at once,but normally tend to be dominated by Strombolian type.Eruption type in fact also can change from older type to new ones as experienced by Merapi volcano.Also can change after a huge destructive eruption occurred as experienced by Tambora and Krakatau which are now on reconstruction phase through their strombolian type of eruption.Some other volcanoes of Indonesia are also still on reconstruction phase.There always be reconstruction after destruction:perhaps that the way volcano works.(Updated:2016).

Contributed By :
Ambo Upe Olenk

REFERENCE:
1.gns.cri.nz/Home/Learning/Science-Topics/Volcanoes/Types-of-Volcanoes-Eruptions
2.liquisearch.com/plinian_eruption/ultra_plinian
3.ekliptika.wordpress.com/2014/02/28/menyaksikan-letusan-plinian-gunung-kelud-dari-keluasan-langit/
4.ekliptika.wordpress.com/2014/02/15/kelud-si-gunung-berapi-penyapu-peradaban/
5.id.wikipedia.org/wiki/Sangeang_Api
6.Data dasar Gunung Api Indonesia 1979
7.GEOMAGZ,Maret 2014
8.GEOMAGZ,Desember 2014
9.GEOMAGZ,Juni 2014
10.Geografi,Syamsudin HS and team,1993

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