In 1883 it is estimated that at least 10% of the deaths were due toįalling tephra and ash flows. Pyroclastic flows traveling across water Island volcanoes sometimes create these flows that travel across the

Sometimes a pyroclastic surge will jump ridges and flow down nearby valleys spreading the destruction into new areas. Where pyroclastic flows travelįollowing the curvature of the land The flows usually follow the curvature of the land to the valleys below the mountain. Takeo, Source mechanism of seismic waves excited by pyroclastic flows observed at Unzen volcano, Japan. Kill or destroy everything in their path. These 'stone winds' traveling at hurricane speeds Temperatures in the flows The temperature inside the flow of hot gases and rock can reach 815° C (1,500 ° F). They usually follow the contour of the land but will sometimes travel over a ridge into nearby valleys. Pyroclastic flows that contain a much higher proportion of gas to rock are known as fully dilute pyroclastic density currents or pyroclastic surges. The flow travels down the slope of the volcano at When part of the eruption column collapses and begins flowing down the * Translated from Journal of Japan Sabo Association, Sabou to Chisui, Vol.81, p.Pyroclastic flows of superheated ash, rock and other debris flow down the side of a volcano at hurricane speeds, USGS Formation and temperatures in pyroclastic flowsįormation of a pyroclastic flow A ground-hugging avalanche of hot ash, pumice, and rock fragments forms 2, these small-scale pyroclastic flows are roughly classified into three types by their origin: a) generated by the non-explosive, gravitational collapse of a lava dome (Merapi type), b) generated by the partial fracture and fall of a lava dome due to a volcanic eruption (Pelée type), and c) generated by the fountain collapse of an eruption column after a volcanic eruption (Soufriere type). In the volcanology, a pyroclastic flow with a bulk volume of 100,000-100 million m3 is called a small-scale pyroclastic flow. They can be described, generally, as hot, gravity. The pyroclastic flow was once called a volcanic clastics flow, but the shortened name 'pyroclastic flow' is used these days. Pyroclastic flows are produced by more violent explosive activity or gravitational dome collapse 11. 2 Generation of pyroclastic flows (by Macdonald)īoth the lower and upper layers are high temperature and high speed. The upper layer is a low-density flow composed of primarily small size volcanic ash that sweeps down the hill floating in the turbulent volcanic gas.įig. A hot (typically >800 ☌), chaotic mixture of rock fragments, gas, and ash that travels rapidly (tens of meters per second) away from a volcanic vent or collapsing flow front. The lower layer is a dense flow composed of relatively large size sediment. In terms of the structure, the pyroclastic flow is roughly divided into the lower layer (debris avalanche) and the upper layer (dust storm), a shown in Fig. Several hazards may affect the area around the volcano, such as lava flows, pyroclastic flows, lahars, jkulhlaups and landslides or debris avalanches. Like other flowing bodies that flow down by gravity, pyroclastic flows flow down topographically low areas, but they easily run over low ridges because their speed is so high. Therefore, even among the sediment-related disasters caused by volcanic eruptions, pyroclastic flows are feared as one of the deadliest phenomena that have devastating impacts on both humans and houses. A combination of high temperature, high speed, and a large volume of sediment causes severe damage to the flowing areas.

In general, the temperature of a pyroclastic flow is as high as 100-1000℃ and its speed is 10-100 m per second or more. A pyroclastic flow refers to a phenomenon in which hot lava pieces, pumices, and ash from a volcanic eruption run down the hillside floating in the generated hot volcanic gas.