ignimbrite A poorly sorted, pyroclastic rock body formed by deposition from a pumiceous pyroclastic flow. The passage of one pyroclastic flow deposits one ignimbrite flow unit with a number of layers directly related to the components of the flow. Ignimbrite flow units deposited by the passage of successive flows can accumulate into a loosely consolidated, composite sheet. Where the rock-body temperature and the accumulating overburden load are both sufficiently high, sintering and flattening of groundmass shards and pumice clasts can occur in the lower part of the body, producing a welded zone within the ignimbrite body which is then characterized by the development of a eutaxitic texture. Hot gases escaping through the ignimbrite deposit can precipitate minerals between the loosely packed shards and pumice in the upper parts of the flow, creating a lithified sillar horizon in which the glass of the pumice and shards is devitrified. Ignimbrites are found on all scales, from a few hundred metres to more than 100 km long, and from one metre to tens of metres thick. The geometry of the ignimbrite sheet is descried using the aspect ratio. See HIGH-ASPECT-RATIO IGNIMBRITE; and LOW-ASPECT-RATIO IGNIMBRITE.
More From encyclopedia.com
Bankfull Flow , bankfull flow Hypopycnal Flow , hypopycnal flow Flow , Flow BIBLIOGRAPHY Embedded within and critical to the burgeoning field of positive psychology, the concept of flow represents an optimal state of con… Debris Flow , Debris flow Debris flow is a process in which water-saturated masses of material ranging from sand grains to boulders move across low slopes. These f… Baseflow , baseflow(dry-weather flow) In a stream or river, the flow of water derived from the seepage of groundwater, and/or through-flow into the surface wate… Lava , Lava Lava is molten rock that has been extruded onto Earth's surface. Before it reaches the surface, lava is called magma . Magma contains crystals ,…
About this article
Updated About encyclopedia.com content Print Article
You Might Also Like