Banyak yang kepingin tahu seperti apa wajah dan bentuk "wedhus" yang ganas ini. Wedhus gembel ini dikenal oleh volcanologist sebagai awan panas. Namun jangan dibayangkan seperti awan putih bersih seperti biri-biri Australi yang lucu.
"Wedhus gembel" merupakan sebuah fenomena khusus dari aktifitas Gunung Merapi di sebelah utara Jogjakarta. Minggu ini berita tentang Merapi dahsyat banget. Meletus berulang-ulang, korban berjatuhan, diawali dengan meninggalnya Mbah Marijan sang Penakluk Gunung Merapi di awal meletusnya 26 Oktober 2010 lalu.
(in memoriam 'Mabah Marijan')
Merapi volcano was born in period of late Pleistocene - Early Holocene. It is situated at the intersection between two main volcanic alignments Ungaran-Telomoyo - Merbabu - Merapi (N164E) and Lawu - Merapi -Sumbing-Sindoro-Slamet or between two main quartenary faults, Semarang fault (north south) and Solo fault (east west). Among them, Merapi volcano is the youngest one.
Awan panas "guguran" results from collapse of lava domes in the crater of the volcano. Occasionally, a dome might grow so large that it becomes unstable and collapses into several drainage catchments. The distance traveled by the flow and its extent depend strongly upon the volume of the destroyed lava, gas pressure and the slope angle of the flank.
Awan panas "letusan" results from collapse of debris that is erupted vertically. Flow direction depends to some extent on the summit morphology.
Most of the Merapi eruption has low explosivity and the awan panas usually reaches about 6 to 7 km from the summit. Some awan panas have traveled as far as 13 km from the summit, such as the deposit generated during the 1969 eruption. Velocity of pyroclastic flow can reach up to 110 km/hour. Infrared spectrometry of carbonized woods sampled from pyroclastic deposits indicates that awan panas have a temperature range of about 3000 - 4000 C.
Some eruptive activities at of the Merapi are characterized by dome formation. A slow upflow of andesitic magma leads to an extrusion of viscous magma, which accumulate and construct a dome in the crater. Magma is almost completely degassed and flows out of the conduit with a rate of up to 20.000 m3/day a normal dome formation. The shape and evolution of the dome depend on the crater configuration. The 1994’s dome stays in a slope of about 350 in the horseshoe shaped crater open to the southwest. The core of the dome is viscous and incandescent (looks glowing at night), while the dome crust is solid.
Written & photos by Edhoy© 2010 by Cyberedhoy Inc, Allrights Reserved