Involcanology, alava dome is a circular, mound-shaped protrusion resulting from the slowextrusion ofviscouslava from avolcano. Dome-building eruptions are common, particularly in convergent plate boundary settings.[1] Around 6% oferuptions on Earth form lava domes.[1] Thegeochemistry of lava domes can vary frombasalt (e.g.Semeru, 1946) torhyolite (e.g.Chaiten, 2010) although the majority are of intermediate composition (such asSantiaguito,dacite-andesite, present day).[2] The characteristic dome shape is attributed to high viscosity that prevents the lava fromflowing very far. This high viscosity can be obtained in two ways: by high levels ofsilica in the magma, or bydegassing of fluidmagma. Since viscousbasaltic andandesitic domesweather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite ordacite.
Lava domes evolve unpredictably, due tonon-linear dynamics caused bycrystallization andoutgassing of the highly viscous lava in the dome'sconduit.[5] Domes undergo various processes such as growth, collapse, solidification anderosion.[6]
Lava domes grow byendogenic dome growth orexogenic dome growth. The former implies the enlargement of a lava dome due to the influx of magma into the dome interior, and the latter refers to discrete lobes of lava emplaced upon the surface of the dome.[2] It is the high viscosity of the lava that prevents it from flowing far from the vent from which it extrudes, creating a dome-like shape of sticky lava that then cools slowly in-situ.[7]Spines andlava flows are common extrusive products of lava domes.[1] Domes may reach heights of several hundred meters, and can grow slowly and steadily for months (e.g.Unzen volcano), years (e.g.Soufrière Hills volcano), or even centuries (e.g.Mount Merapi volcano). The sides of these structures are composed of unstable rock debris. Due to the intermittent buildup of gaspressure, erupting domes can often experience episodes ofexplosive eruption over time.[8] If part of a lava dome collapses and exposes pressurized magma,pyroclastic flows can be produced.[9] Other hazards associated with lava domes are the destruction of property fromlava flows,forest fires, andlahars triggered from re-mobilization of loose ash and debris. Lava domes are one of the principal structural features of manystratovolcanoes worldwide. Lava domes are prone to unusually dangerous explosions since they can contain rhyoliticsilica-rich lava.
Characteristics of lava dome eruptions include shallow, long-period and hybridseismicity, which is attributed to excess fluid pressures in the contributing vent chamber. Other characteristics of lava domes include their hemispherical dome shape, cycles of dome growth over long periods, and sudden onsets of violent explosive activity.[10] The average rate of dome growth may be used as a rough indicator ofmagma supply, but it shows no systematic relationship to the timing or characteristics of lava dome explosions.[11]
The bulging cryptodome of Mt. St. Helens on April 27, 1980
Acryptodome (from theGreekκρυπτός,kryptos, "hidden, secret") is a dome-shaped structure created by accumulation ofviscousmagma at a shallow depth.[13] Two examples of cryptodomes were the ones leading to the 1956 eruption ofBezymianny and the1980 eruption of Mount St. Helens. In each case, the explosive eruption began after the cryptodome caused the side of the volcano to bulge outward and led to asector collapse, in turn leading toexplosive decompression of the subterranean cryptodome.[14][15]
Soufrière Hills lava spine before the 1997 eruption Lava dome growth during the 2004–2008 eruptive phase of Mount St Helens
A lava spine or lava spire is a growth that can form on the top of a lava dome. A lava spine can increase the instability of the underlying lava dome. A recent example of a lava spine is the spine formed in 1997 at theSoufrière Hills Volcano on Montserrat.
Coulées (or coulees) are lava domes that have experienced some flow away from their original position, thus resembling both lava domes andlava flows.[2]
The world's largest knowndacite flow is theChao dacite dome complex, a huge coulée flow-dome between two volcanoes in northernChile. This flow is over 14 kilometres (8.7 mi) long, has obvious flow features like pressure ridges, and a flow front 400 metres (1,300 ft) tall (the dark scalloped line at lower left).[16] There is another prominent coulée flow on the flank ofLlullaillaco volcano, inArgentina,[17] and other examples in theAndes.
^abcFink, Jonathan H.; Anderson, Steven W. (2001). "Lava Domes and Coulees". In Sigursson, Haraldur (ed.).Encyclopedia of Volcanoes.Academic Press. pp. 307–19.
^Newhall, C.G.; Melson., W.G. (September 1983), "Explosive activity associated with the growth of volcanic domes",Journal of Volcanology and Geothermal Research,17 (1–4):111–131,Bibcode:1983JVGR...17..111N,doi:10.1016/0377-0273(83)90064-1
^Goto, Yoshihiko; Tsuchiya, Nobutaka (July 2004). "Morphology and growth style of a Miocene submarine dacite lava dome at Atsumi, northeast Japan".Journal of Volcanology and Geothermal Research.134 (4):255–275.Bibcode:2004JVGR..134..255G.doi:10.1016/j.jvolgeores.2004.03.015.
