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cognate or accessory particles – older volcanic rocks from the same volcano accidental particles – derived from the rocks under the volcano These particles may vary in size; tephra can range from ash (< 1 / 10 inch [0.25 cm]) or lapilli (little stones from 1 / 10 to 2 + 1 ⁄ 2 inches or 0.25 to 6.35 centimetres) to volcanic bombs (>2.5 ...
First: volcanic arc, volcanic belt and volcanic zone. Second: volcanic area, caldera cluster and caldera complex. Third: volcanic field, volcanic system and volcanic center. A volcanic field is a localized area of the Earth's crust that is prone to localized volcanic activity.
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.
Plinian/Vesuvian eruptions are marked by columns of volcanic debris and hot gases ejected high into the stratosphere, the second layer of Earth's atmosphere. The key characteristics are the ejection of a large amount of pumice and very powerful continuous gas-driven eruptions.
The interaction between the magma, expanding steam, and volcanic gases resulted in the production and ejection of fine-grained pyroclastic debris called ash with the consistency of flour. The volcanic ash comprising a tuff cone accumulated either as fallout from eruption columns, from low-density volcanic surges and pyroclastic flows, or ...
Pyroclastic rocks are often the result of volcanic debris, such as ash, bombs and tephra, and other volcanic ejecta. Examples of pyroclastic rocks are tuff and ignimbrite. [citation needed] Shallow intrusions, which possess structure similar to volcanic rather than plutonic rocks, are also considered to be volcanic, shading into subvolcanic.
A pyroclastic surge is a fluidised mass of turbulent gas and rock fragments that is ejected during some volcanic eruptions.It is similar to a pyroclastic flow but it has a lower density or contains a much higher ratio of gas to rock, [1] which makes it more turbulent and allows it to rise over ridges and hills rather than always travel downhill as pyroclastic flows do.
A volcanic hazard is the probability a volcanic eruption or related geophysical event will occur in a given geographic area and within a specified window of time. The risk that can be associated with a volcanic hazard depends on the proximity and vulnerability of an asset or a population of people near to where a volcanic event might occur.