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Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 2018. A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) [1] is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of 100 km/h (30 m/s; 60 mph) but is capable of reaching speeds up to ...
The word lava comes from Italian and is probably derived from the Latin word labes, which means a fall or slide. [2] [3] An early use of the word in connection with extrusion of magma from below the surface is found in a short account of the 1737 eruption of Vesuvius, written by Francesco Serao, who described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of ...
The lava continues to flow this way until it begins to block its source. At this point, the subsurface lava is still hot enough to break out at a point, and from this point the lava begins as a new "source". Lava flows from the previous source to this breakout point as the surrounding lava of the pāhoehoe flow cools.
However, rhyolite lavas occasionally erupt effusively to form lava spines, lava domes or "coulees" (which are thick, short lava flows). [22] The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian. [23] Felsic lavas can erupt at temperatures as low as 800 °C (1,470 °F). [24]
The Greenstone Flow is one of the world's largest known lava flows, estimated at a volume ~1650 to ~6000 cubic kilometers of mafic lava. [2] [3] In places, the lava pooled to depth of 487 meters. [4] The flow was generated by a flood basalt eruption during the Midcontinental Rift, which occurred 1.1 billion years ago. [5]
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 ...
The gas released at the surface has a composition that is a mass-flow average of the magma exsolved at various depths and is not representative of the magma conditions at any one depth. Molten rock (either magma or lava) near the atmosphere releases high-temperature volcanic gas (>400 °C).
The two main types of lava field structures are defined as sheet flow lava and pillow lava. Sheet flow lava appears like a wrinkled or folded sheet, while pillow lava is bulbous, and often looks like a pile of pillows atop one another. [2] An important aspect of lava flow morphology is a phenomenon known as lava flow inflation. This occurs in ...