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Lahars are described as 'primary' or 'syn-eruptive' if they occur simultaneously with or are triggered by primary volcanic activity. 'Secondary' or 'post-eruptive' lahars occur in the absence of primary volcanic activity, e.g. as a result of rainfall during pauses in activity or during dormancy. [5] [6]
Lahars travelled as fast as 90 mph (140 km/h) while still high on the volcano, but progressively slowed to about 3 mph (4.8 km/h) on the flatter and wider parts of rivers. [9] Mudflows from the southern and eastern flanks had the consistency of wet concrete as they raced down Muddy River, Pine Creek, and Smith Creek to their confluence at the ...
Since the eruption, each heavy rain has brought massive lahars from the volcano, displacing thousands of people and inflicting extensive damage to buildings and infrastructure costing billions to repair. Funds were spent constructing dikes and dams to control post-eruption lahar flows. [21]
Mount Rainier, a snowcapped volcano, looms over Puyallup Valley near Orting, Washington. The prospect of a lahar — a swiftly moving debris flow caused by melting snow and ice typically during a ...
During Sugar Bowl time, the volcano first erupted quietly to produce a dome, then erupted violently at least twice producing a small volume of tephra, directed-blast deposits, pyroclastic flows, and lahars. [32] East Dome, a small hypersthene-homblende dacite dome on the east slope of the volcano, was likely formed around the Sugar Bowl period ...
Some of the eruptive structures formed during volcanic activity (counterclockwise): a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption. Several types of volcanic eruptions—during which material is expelled from a volcanic vent or fissure—have been distinguished by volcanologists.
Nevado del Ruiz has erupted several times since 1985, and continues to threaten up to 500,000 people living along the Combeima, Chinchiná, Coello-Toche, and Guali river valleys. A lahar (or group of lahars) similar in size to the 1985 event might travel as far as 100 km (60 mi) from the volcano and could be triggered by a small eruption.
Not all lahars are this big, and they can occur while a volcano is still erupting. During the La Soufrière eruption on the island of St. Vincent, a dry river bed was filled with mud and debris ...