|
A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow"〔3 meters/minute to 5 meters/second; , citing Cruden and Varnes, 1996.〕 of debris that has become partially or fully liquified by the addition of significant amounts of water to the source material.〔; .〕 Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows; thus, they are able to travel farther and across lower slope angles. Both types are generally mixtures of various kinds of materials of different sizes, which are typically sorted by size upon deposition.〔.〕 Mudflows are often called ''mudslides'', a term applied indiscriminately by the mass media to a variety of mass wasting events.〔.〕 Mudflows often start as slides, becoming flows as water is entrained along the flow path; such events are often called ''flow slides''.〔; .〕 Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of stratovolcanoes) and jökulhlaups (outbursts from under glaciers or icecaps).〔.〕 == Triggering of mudflows == Heavy rainfall, snowmelt, or high levels of ground water flowing through cracked bedrock may trigger a movement of soil or sediments. Floods and debris flows may also occur when strong rains on hill or mountain slopes cause extensive erosion and/or what is known as "channel scour". The 2006 Sidoarjo mud flow may have been caused by rogue drilling. Some broad mudflows are rather viscous and therefore slow; others begin very quickly and continue like an avalanche. If large enough, they can devastate villages and countrysides. They are composed of at least 50% silt and clay-sized materials and up to 30% water. Mudflows are common even in the hills around Los Angeles, California, where they have destroyed many homes built on hillsides without sufficient support after fires destroy vegetation holding the land. The point where a muddy material begins to flow depends on its grain size and the water content. Fine grainy material or soil has a smaller friction angle than a coarse sediment or a debris flow, but falling rock pieces can trigger a material flow, too. On December 14, 1999 in Vargas, Venezuela, a mudflow known as The Vargas tragedy significantly altered more than 60 kilometers (37 mi) of the coastline. It was triggered by heavy rainfall and caused estimated damages of US$1.79 to US$3.5 billion, killed between 10,000 and 30,000 people, forced 85,000 people to evacuate, and led to the complete collapse of the state's infrastructure. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mudflow」の詳細全文を読む スポンサード リンク
|