What is pyroclastic flow in geography

pyroclastic flow

pyroclastic flow, turbulent to laminar flowing, dense dispersion of hot gas, magma shreds or lava fragments, crystals and possibly rock fragments, which move on the land surface following the topography (Fig.). Pyroclastic currents can a) arise from the (partial) collapse of eruption clouds, whereby the still molten or already solidified magma fragments are usually strongly foamed (pumice). The result is streams rich in pumice, the deposits of which are known as ignimbrites. b) They can also be the result of an explosion or a gravitational collapse of SiO2- be rich lava domes and lava fronts. This creates block-and-ash flows, the deposits of which are referred to as block-and-ash flow deposits.

pyroclastic flow: Build-up and deposits of a pyroclastic flow. The pyroclastic flow (2) is encased in an ash cloud (3a, 3b), which consists of heated air and ash particles escaping from the flow and hot gas. Gas and ash can also shoot out at the current front and form a partially sloping basal layer (ground-surge deposit, 1). The ash cloud gradually sediments on the massive stream deposit (2) as a fine fall deposit (3b). Lateral currents at the base of the ash cloud can create ash cloud surge deposits (3a). pyroclastic flow: