Dense-rock equivalent

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Dense-rock equivalent (DRE) is a volcanologic calculation used to estimate volcanic eruption volume. One of the widely accepted measures of the size of a historic or prehistoric eruption is the volume of magma ejected as pumice and volcanic ash, known as tephra during an explosive phase of the eruption, or the volume of lava extruded during an effusive phase of a volcanic eruption. Eruption volumes are commonly expressed in cubic kilometers (km3).

Historical and geological estimates of tephra volumes are usually obtained by mapping the distribution and thickness of tephra deposits on the ground after the eruption is over. For historical volcanic explosions, further estimates must be made of tephra deposits that might have changed significantly over time by other geological processes including erosion. Tephra volumes measured in this way must then be corrected for void spaces (vesicles – bubbles within the pumice, empty spaces between individual pieces of pumice or ash) to get an estimate of the original volume of magma erupted. This correction can be made by comparing the bulk density of the tephra deposit with the known density of the original gas-free rock-type that makes up the tephra. The result is referred to as the dense-rock equivalent of the erupted volume. [1]

Dense-rock equivalent calculations can also be used to measure the sizes of volcanic eruptions on other planetary bodies, such as Mars. [2] However, the challenge to making these estimates is accurately estimating the density of the tephra deposit or of the dense rock, measuring the thickness of tephra, determining if the tephra is related to the eruption studied or to a nearby one, and estimating changes resulting from other geological processes that may be less understood than on Earth.

Significant studies of the dense-rock equivalent erupted volumes of the Bronze-Age Minoan eruption in Santorini have provided data to archeologists to better understand the effect of the eruption on development of several civilizations including Ancient Greek and Ancient Egyptian cultures. Through careful analysis of pumice and ash deposits (including deep sea core samples), researchers have been able to make dense-rock equivalent volume estimates for each of the major eruptions of Thera. [3] [4]

See also

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Mount Vesuvius Active stratovolcano in the Gulf of Naples, Italy

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Stratovolcano Tall, conical volcano built up by many layers of hardened lava and other ejecta

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Pumice Light coloured highly vesicular volcanic rock

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Mount Mazama Complex volcano in the Cascade Range

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Minoan eruption

The Minoan eruption was a major catastrophic volcanic eruption that devastated the Aegean island of Thera in around 1600 BCE. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on nearby islands and the coast of Crete with subsequent earthquakes and tsunamis. With a VEI magnitude between 6 and 7, resulting in an ejection of approximately 60 km3 (14 cu mi) of dense-rock equivalent (DRE), the eruption was one of the largest volcanic events on Earth in human history.

A pyroclastic fall is a uniform deposit of material which has been ejected from a volcanic eruption or plume such as an ash fall or tuff. Pyroclastic air fall deposits are a result of:

  1. Ballistic transport of ejecta such as volcanic blocks, volcanic bombs and lapilli from volcanic explosions
  2. Deposition of material from convective clouds associated with pyroclastic flows such as coignimbrite falls
  3. Ejecta carried in gas streaming from a vent. The material under the action of gravity will settle out from an eruption plume or eruption column
  4. Ejecta settling from an eruptive plume or eruption column that is displaced laterally by wind currents and is dispersed over great distances
Nazko Cone

Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic Belt. The small tree-covered cone rises 120 m above the Chilcotin-Nechako Plateau and rests on glacial till. It was formed in three episodes of activity, the first of which took place during the Pleistocene interglacial stage about 340,000 years ago. The second stage produced a large hyaloclastite scoria mound erupted beneath the Cordilleran Ice Sheet during the Pleistocene. Its last eruption produced two small lava flows that traveled 1 km to the west, along with a blanket of volcanic ash that extends several km to the north and east of the cone.

Types of volcanic eruptions mechanisms of eruption

Several types of volcanic eruptions—during which lava, tephra, and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

Phreatomagmatic eruption Volcanic eruption involving both steam and magma

Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions contain juvenile (magmatic) clasts. It is common for a large explosive eruption to have magmatic and phreatomagmatic components.

Kolumbo Active submarine volcano in the Agean Sea near Santorini

Kolumbo is an active submarine volcano in the Aegean Sea, about 8 km northeast of Cape Kolumbo, Santorini island. The largest of a line of about twenty submarine volcanic cones extending to the northeast from Santorini, it is about 3 km in diameter with a crater 1.5 km across. It was "discovered" when it breached the sea surface in 1649-50, but its explosion was not to be compared to the well-known Thera explosion and caldera collapse, currently dated ca. 1630 BCE, with its devastating consequences for Minoan civilization. The Smithsonian Institution's Global Volcanism Program treats it as part of the Santorini volcano.

Taupo Volcano Volcanic crater lake in New Zealand

Lake Taupo, in the centre of New Zealand’s North Island, is the caldera of a large rhyolitic supervolcano called the Taupo Volcano. This huge volcano has produced two of the world’s most violent eruptions in geologically recent times.

Bridge River Vent

The Bridge River Vent is a volcanic crater in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. It is located 51 km (32 mi) west of Bralorne on the northeastern flank of the Mount Meager massif. With an elevation of 1,524 m (5,000 ft), it lies on the steep northern face of Plinth Peak, a 2,677 m (8,783 ft) high volcanic peak comprising the northern portion of Meager. The vent rises above the western shoulder of the Pemberton Valley and represents the northernmost volcanic feature of the Mount Meager massif.

Volcanic ash Natural material created during volcanic eruptions

Volcanic ash consists of fragments of rock, minerals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products, including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the gasses shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometres away.

The 946 eruption of Paektu Mountain in Korea and China, also known as the Millennium Eruption or Tianchi eruption, was one of the most powerful volcanic eruptions in recorded history and is classified as a VEI 7 event. The eruption resulted in a brief period of significant climate change in Manchuria. The year of the eruption has not been precisely determined, but a possible year is A.D. 946.

Campanian Ignimbrite eruption VEI 7.7-7.8 Volcanic eruption around 40,000 years BP

The Campanian Ignimbrite eruption was a major volcanic eruption in the Mediterranean during the late Quaternary, classified at 7 on the Volcanic Explosivity Index (VEI). The event has been attributed to the Archiflegreo volcano, the 13-kilometre-wide (8.1 mi) caldera of the Phlegraean Fields, located 20 km (12 mi) west of Mount Vesuvius under the western outskirts of the city of Naples and the Gulf of Pozzuoli, Italy. Estimates of the date, magnitude and the amount of ejected material have varied considerably during several centuries of investigation. This applies to most significant volcanic events that originated in the Campanian Plain, as it is one of the most complex volcanic structures in the world. However, continued research, advancing methods and accumulation of volcanological, geochronological, and geochemical data has amounted to ever more precise dating.

Aspronisi

Aspronisi is an uninhabited island lying within the Santorini caldera. The island was originally formed by the massive Minoan eruption in the 2nd millennium BC, after which it was gradually built up by successive volcanic activity. The name Aspronisi, which means 'White Island' in Greek, is derived from the island being partially composed of white pumice.

References

  1. ↑ "A Note on Eruption Sizes". Long Valley Observatory Volcano Hazards Program. U.S. Geological Survey. 1999-11-30. Archived from the original on 2007-02-04. Retrieved 2007-03-15.
  2. ↑ Wilson, L; Mouginis-Mark, PJ (2001). "Estimation of volcanic eruption conditions for a large flank event on Elysium Mons, Mars". Journal of Geophysical Research. 106 (E9): 20621–20628. Bibcode:2001JGR...10620621W. doi: 10.1029/2000JE001420 . Retrieved 2007-04-15.
  3. ↑ Pyle, DM (1989). Thera and the Aegean World III. Volume Two: "Earth Sciences" Proceedings of the Third International Congress, Santorini, Greece, 3–9 September 1989. The Thera Foundation. pp. 113–121. ISBN   0-9506133-5-5. Archived from the original on 21 August 2007. Retrieved 2007-08-05.
  4. ↑ Watkins, ND; Sparks, RSJ; Sigurdsson, H; Huang, TC; Federman, A; Carey, S; Ninkovich, D (1978). "Volume and extent of the Minoan tephra from Santorini Volcano: new evidence from deep-sea sediment cores". Nature. 271 (5641): 122–126. Bibcode:1978Natur.271..122W. doi:10.1038/271122a0.
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