BENTUKLAHAN ASAL VULKANIS

Vulkanisme : Berbagai penomena yang berkaitan dengan gerakan magma kepermukaan bumi

DISTRIBUSI VULKANOLocation of the Earth's major volcanoes. Most occur along tectonic plate boundaries where plate subduction creates rising plumes of magma. The volcanoes that do not occur along plate boundaries are the result of localized asthenosphere hot spots that melt through the Earth's crust. The Hawaiian Island chain of volcanoes was create by a hot spot.

Vulkano : Gundukan atau kerucut yang tersusun atas batuan beku lelehan atau bahan klastisSmoking Bromo and Semeru (background) volcanoes on Java in Indonesia.

Lava intruded into fissures solidifies to form dikes, sill.

Nonexplosive eruption. Low viscosity basaltic lava flow from an active volcano on one of the Hawaiian Islands. TYPES OF ERUPTIONS

An eruption on Klauea, Hawaii TYPES OF ERUPTIONSExplosive eruption being associated with the emission or acid magmas.

ERUPTIONTwo distinct modes of solidification are exhibited by flowing lava. There are most commonly referred to as pahoehoe & aa types of solidificationLava menuju kepermukaan bumi

Phoehoe (Hawaiian English, from Hawaiian, meaning "smooth, unbroken lava") is basaltic lava that has a smooth, billowy, undulating, or ropy surface. Toes of a phoehoe advance across a road in Kalapana on the east rift zone of Klauea Volcano in Hawaii. ERUPTION

'A' (Hawaiian English, from Hawaiian meaning "stony with rough lava", but also to "burn" or "blaze"). 'A' is characterized by a rough or rubbly surface composed of broken lava blocks called clinker ERUPTIONGlowing a flow front advancing over phoehoe on the coastal plain of Klauea in Hawaii

A dark tephra cloud rises from a large methane gas explosion in front of a slow-moving `a`a flow on Mauna Loa Volcano, Hawai`iERUPTION'A' Lava

Erupsi : Proses keluarnya material gunungapi kepermukaan bumi akibat tekanan dari dalam bumi melalului celah atau lubangTYPES OF ERUPTIONS Hawaiian Strombolian Vulcanian Pelean

ERUPTIONSThe Hawaiian type of eruption is marked by much fluid, effusive, basaltic lava. Scoria mounds may be built around lava vents. Lava rarely pours out of the crater but more commonly issues through fissures around the sides of the volcanic pile as flank eruption

ERUPTIONStrue strombolian activity is characterized by short-lived, explosive outbursts of pasty lava ejected a few tens or hundreds of meters into the air. Although Strombolian eruptions are much noisier than Hawaiian eruptions, they are no more dangerous. eruptions produce little or no flowing lava.

However, during the end stages of scoria-cone formation, it is not unusual for Strombolian activity to wane and give way to the calm extrusion of basaltic lava flows. As a general rule, a'a lava flows appear to be more common than the more fluid pahoehoe types. ERUPTIONSStrombolian activity from Mt. Etna in October 2002.

ERUPTIONSVulcanian eruption eject viscous lavas which do not remain liquid long after coming in contact with air. The lava crusts over between eruptions, and each new explosion causes fragmentation of this frozen crust. Much ash is emitted, and ash-laden gases rise to form large dark cauliflower-like clouds.

ERUPTIONSPelean eruption the lava is extremely viscous and violent explosions are characteristic. These glowing clouds consist of a mixture of extremely hot, incandescent fine ash and coarser rock fragments permeated with hot gases o form a short emulsion

ERUPTIONSCENTRAL ERUPTIONS are eruption which take place through circumcribed ventsFISSURE ERUPTION are eruption which take place along a fissure or series of fissures

The rock fragments ejected during explosive activity are known as pyroclastic materials, they are : Volcanic dust, volcanic ash, lapilli, scoriae, bombs, and blockMount St. Helens eruption on May 18, 1980.

Thurston Lava Tube in Hawaii Volcanoes National Park. The step mark on the right wall indicates the depth at which the lava flowed for a period of time LAVA TUBES are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel. ERUPTION

The walls of this inactive lava channel record the different heights of the lava surface during the flow's waning stagesFEATURES OF LAVA FIELDLAVA CHANNELthe surface of an `a`a flow on Kilauea Volcano, Hawai`i.

TYPES OF VOLCANOES4 Type of volcano :Basalt cone Basalt dome or Shield volcanoesCinder coneStrato volcano

TYPES OF VOLCANOESBASALT CONE are lower cones because of the fluidity of basaltic lava.

TYPES OF VOLCANOESA SHIELD VOLCANO is a wide volcano with shallowly-sloping sides. Its formed by lava flows of low viscosity lava that flows easily. Consequently, a volcanic mountain having a broad profile is built up over time by flow after flow of relatively fluid basaltic lava issuing from vents or fissures on the surface of the volcanoMauna Kea, a shield volcano, on the Island of Hawaii with a light dusting of snow.

A CINDER CONE is a small volcano, between 100 and 400 meters tall, made up of exploded rock blasted out of a central vent at a high velocity. These volcanoes develop from magma of basaltic to intermediate composition (andesite). Cinder cone volcano. Note how the vegetation near the mound has been burnt by lava flows. TYPES OF VOLCANOES

TYPES OF VOLCANOESA STRATO VOLCANO is a tall, conical volcano composed of many layers of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. Mount Merapi in August 2003 showing steam venting from the crater.

A Strato-volcano exhibits through stratification produced by alternating sheets of lava & pyroclastic materialMt. Rainier, a stratovolcano in Washington Popocatpetl, an active stratovolcano in MexicoTYPES OF VOLCANOES

Consolidated pyroclastic flow deposits of Bukit ASH SHOWER. One of chief product of vulcanian & pelean types of eruptions is volcanic ash. Ash shower are commonly cold.

VOLCANIC MUDFLOWS OR LAHAR is a type of mudflow composed of pyroclastic material and water that flows down from a volcano, typically along a river valley. Lahars have the consistency of concrete: fluid when moving, then solid when stopped. large lahars can flow several tens of meters per second, and can flow for many kilometres, causing catastrophic destruction along the way. Lahar from a March 1982 eruption of Mount St. Helens.

A PLUG DOME OR LAVA DOME is mound-shaped growth resulting from the eruption of high-silica lava (usually rhyolite and/or dacite) from a volcano. The high silica content makes the lava very viscous, so that it cannot flow very far from its vent before solidifying. Lava domes are one of the principal structural features of many stratovolcanoes worldwide. One of the Mono Craters, an example of a rhyolite dome.

Domes may reach heights of several hundred metres, and can grow slowly and steadily for months or years. lava domes can be unstable and prone to collapse. A PLUG DOME OR LAVA DOMENovarupta rhyolite lava dome in Katmai National Park, Alaska. It was the source vent for a major eruption in 1912, causing the summit of nearby Katmai to collapse and creating the Valley of Ten Thousand Smokes.

Summit Crater VOLCANIC CRATERS may result from either explosif activity or from susidence. Expulsion of volcanic ash, lapili & other forms of ejecta may build a ring about volcanic vent & produce a crater.

A CALDERA is a volcanic feature formed by the collapse of a volcano into itself, making it a large, special form of volcanic crater. Calderas may be filled with water, creating crater lakesCrater Lake, OregonA caldera is a volcanic feature formed by the collapse

VOLCANIC NECK may be all that is left of former volcnic cones & dome in old age. One of volcanic neck is Devil tower. Presumably, if Devils Tower was a volcanic plug, any volcanics created by it (volcanic ash, lava flows, volcanic debris) would have been eroded away long ago. Devils Tower National Monument