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Large lahars hundreds of metres wide and tens of metres deep can flow several tens of metres per second (22 mph or more), much too fast for people to outrun. [9] On steep slopes, lahar speeds can exceed 200 kilometres per hour (120 mph). [9] A lahar can cause catastrophic destruction along a potential path of more than 300 kilometres (190 mi). [10]
These eruptions wear down the lava dome holding the magma down, and it disintegrates, leading to much more quiet and continuous eruptions. Thus an early sign of future Vulcanian activity is lava dome growth, and its collapse generates an outpouring of pyroclastic material down the volcano's slope. [24] Tavurvur in Papua New Guinea erupting
Later that day, Subandrio, head of the BPPTK suggested there would be further eruptions as magma continued to push its way up into the volcano's lava dome. [16] [17] A pyroclastic river flowed from Merapi again on 30 October 2010 at 00:35. A pyroclastic flow headed toward Gendol River, Kuning River, Krasak River, and Boyong River.
Because the dome sits at the lip of a steep slope leading out of the crater it can become unstable, and (as in 1990) collapse into the Drift River valley, producing avalanches of hot lava blocks, pyroclastic flows, lahars, and ash columns tens of thousands of feet tall, which can carry ash to Alaska communities.
Subglacial eruptions, those of ice-covered volcanoes, result in the interaction of magma with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcanic areas, including Iceland, Alaska, and parts of the Andes.
Low-silica magma is more fluid and usually erupts as lava in less explosive eruptions than dacite because gas and water vapor escape easily from it. Eruptions of basalt magma typically produce elongate lava flows, as well as build cinder cones (piles of small frothy lava fragments or 'cinders') around volcanic vents. [4]
In the broad sense [2] [4] of the term, volcaniclastics includes pyroclastic rocks such as the Bandelier Tuff; [5] cinder cones and other tephra deposits; the basal and capping breccia that characterize ʻaʻā lava flows; and lahars and debris flows of volcanic origin. [6] Volcaniclastics make up more of the volume of many volcanoes than do ...
It is likely that the lava spreads by a process of inflation in which the lava moves beneath a solid insulating crust, which keeps it hot and mobile. [36] Studies of the Ginkgo flow of the Columbia River Plateau, which is 30 to 70 meters (98 to 230 ft) thick, show that the temperature of the lava dropped by just 20 °C (68 °F) over a distance ...