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Pyroclastics ("fire fragments) Tephra = volcanic fragments of all sizes: dust (smallest)ashcinderslapillivolcanic bombs (largest)GL-2241

Material PiroklastikUkuran < 4mm: ash; 4-32 mm lapilli; >32 mm, blocksTephra: piroklastik yang dilontarkan dari gunungapi dan belum sempat membentuk agregat.Lahars: - Mudflows, tersusun atas partikel berukuran debu (ash).-Bergerak dengan kecepatan 60-100 mph-Misal letusan St. Helens, kerusakan yang diakibatkan oleh mudflow.GL-2241

Pyroclastic eruptions style: extremely violenteruption type: Plinian landforms: composite volcano; pyroclastic flowsexamples Mt. St. Helens, WA; Mt. Pinatubo

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Skematik Pengendapan Piroklastik (Menurut Walker, 1983) GL-2241

Bagan Alir Analisa Laboratorium Untuk Piroklastik (Menurut Wohletz dan Heiken,1992) GL-2241

Diagram Skematik Suatu Endapan Aliran Piroklastik (Menurut Cas dan Wright, 1988) GL-2241

PYROCLASTIC FALLCharacterized by their relatively well sorted size.The emplacement characteristics of these deposits are controlled by the terminal fall velocities of individual pyroclasts (Walker et al.,1971; Wilson, 1972).

PYROCLASTIC FLOWSComprise some of the most voluminous explosive products.One possible emplacement model is that for the gravitational collapse of an eruptive column (Wright, 1979).

PYROCLASTIC SURGERelatively thin bedding (generally less than a decimeter)Indicate unsteady flow and rapid variations in particle to gas volume ratios.Explosive hydrovolcanic activity (Waters and Fisher, 1971)

EQUATION OF MOTION FOR AN ERUPTIVE COLUMN(WILSON, 1976)q=a ratio of the average column velocity to its centerline velocityRhob=Bulk density of the columnRv=Vent radiusRhoa=Density of the ambient air

Schematic of an idealized volcanic eruptive system(Adapted from Wilson et al., 1980)Although analytical solutions for subsurface flow of magma and volatiles can be made, the exact physical conditions of this flow are unknown, and this lack of information limits the calculation of mass and energy transport within the erupted jet and plume.

Pyroclastic flow deposit on Merapi. Photo by Jack Lockwood, U.S. Geological Survey, November 2, 1982.

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Volcanic ashVolcanic ash consists of rock, mineral, and volcanic glass fragments smaller than 2 mm (0.1 inch) in diameter, which is slightly larger than the size of a pinhead. Volcanic ash is not the same as the soft fluffy ash that results from burning wood, leaves, or paper. It is hard, does not dissolve in water, and can be extremely small--ash particles less than 0.025 mm (1/1,000th of an inch) in diameter are common.

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TEPHRAGL-2241

Tephra deposit about 9 cm thick blankets former U.S. Clark Air Base, Philippines, about 25 km east of Mount Pinatubo. The pumice and ash fell to the ground on June 15 during the climactic eruption of Pinatubo. During the eruption, a massive typhoon made landfall and passed about 75 km northeast of the volcano.

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Tephra block (also called a ballistic) on the crater floor of Mount St. Helens about 100 m from the lava dome. This lava fragment was blasted from the dome by a short-lived explosion caused by either (1) a vigorous release of gas from magma within or beneath the dome; or (2) by superheated groundwater "flashing" to steam. The rock broke apart when it landed on the crater floor. Note black camera lense cap for scale.

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Tephra covers the Crater Rim Drive Road and has stripped leaves and branches from the forest. The trees, though almost entirely defoliated, survived the eruption and flourish today

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Layer of tephra consisting of accretionary lapilli surrounded by wind-deposited ash in the Ka`u Desert, Kilauea Volcano. This layer is one of several found at this location, about 10 km from Kilauea's summit caldera.

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LAHARSGL-2241

Lahar = volcanic mudflow composed of ash and water; consistency of wet concrete; will follow river channelsArmero, ColumbiaNevado del RuizGL-2241

Dark pathways created by lahars streak the sides of Mount St. Helens during its catastrophic eruption on May 18, 1980. The lahars were triggered by the sudden melting of snow and ice from hot volcanic rocks ejected by the initial explosive activity and subsequent pyroclastic flows.

Mount St. Helens, WashingtonGL-2241

The human consequences of these post-eruption lahars at Mount Pinatubo have been enormous. In the first five years following the eruption, lahars destroyed the homes of more than 100,000 people; each year during the rainy seasons, the threat of lahars forced another 100,000 people to evacuate their homes and farmland. Lahars also covered about 120,000 hectacres (roughly 300,000 acres) with sediment to an average depth of about one meter, and floods spread rock debris over an area at least several times larger. GL-2241

LapilliRock fragments between 2 and 64 mm (0.08-2.5 in) in diameter that were ejected from a volcano during an explosive eruption are called lapilli. Lapilli (singular: lapillus) means "little stones" in Italian. Lapilli may consist of many different types of tephra, including scoria, pumice, and reticulite.

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Accretionary lapilliRounded tephra balls between 2 and 64 mm in diameter are called accretionary lapilli if they consist of tiny ash particles. Volcanic ash sometimes form such balls in an eruption column or cloud, owing to moisture or electrostatic forces. Lapilli (singular: lapillus) means "little stones" in Italian.

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