In volcanology, a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on Earth form lava domes. The geochemistry of lava domes can vary from basalt (e.g. Semeru, 1946) to rhyolite (e.g. Chaiten, 2010) although the majority are of intermediate composition (such as Santiaguito, dacite-andesite, present day). The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite.
Existence of lava domes has been suggested for some domed structures on the Moon, Venus, and Mars, e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum.
Dome dynamics
Lava domes evolve unpredictably, due to non-linear dynamics caused by crystallization and outgassing of the highly viscous lava in the dome's conduit. Domes undergo various processes such as growth, collapse, solidification and erosion.
Lava domes grow by endogenic dome growth or exogenic 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. 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. Spines and lava flows are common extrusive products of lava domes. 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 gas pressure, erupting domes can often experience episodes of explosive eruption over time. If part of a lava dome collapses and exposes pressurized magma, pyroclastic flows can be produced. Other hazards associated with lava domes are the destruction of property from lava flows, forest fires, and lahars triggered from re-mobilization of loose ash and debris. Lava domes are one of the principal structural features of many stratovolcanoes worldwide. Lava domes are prone to unusually dangerous explosions since they can contain rhyolitic silica-rich lava.
Characteristics of lava dome eruptions include shallow, long-period and hybrid seismicity, 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. The average rate of dome growth may be used as a rough indicator of magma supply, but it shows no systematic relationship to the timing or characteristics of lava dome explosions.
Gravitational collapse of a lava dome can produce a block and ash flow.
Related landforms Cryptodomes
A cryptodome (from the Greek , , "hidden, secret") is a dome-shaped structure created by accumulation of viscous magma at a shallow depth. Two examples of cryptodomes were the ones leading to the 1956 eruption of Bezymianny and the 1980 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 a sector collapse, in turn leading to explosive decompression of the subterranean cryptodome.
Lava spine/Lava spire
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 the Soufrière Hills Volcano on Montserrat.
Lava coulées
Coulées (or coulees) are lava domes that have experienced some flow away from their original position, thus resembling both lava domes and lava flows.
The world's largest known dacite flow is the Chao dacite dome complex, a huge coulée flow-dome between two volcanoes in northern Chile. This flow is over long, has obvious flow features like pressure ridges, and a flow front tall (the dark scalloped line at lower left).Chao dacite dome complex at NASA Earth Observatory There is another prominent coulée flow on the flank of Llullaillaco volcano, in Argentina,Coulées! by Erik Klemetti, an assistant professor of Geosciences at Denison University. and other examples in the Andes.
Examples of lava domes
+ Lava domes Name of lava dome Country Volcanic area Composition Last eruptionor growth episode Bijang Philippines Macolod Corridor Dacite 66 ± 14ka Chaitén lava dome Chile Southern Volcanic Zone Rhyolite 2009 Ciomadul lava domes Romania Carpathians Dacite Pleistocene Cordón Caulle lava domes Chile Southern Volcanic Zone Rhyolite 2012 Galeras lava dome Colombia Northern Volcanic Zone Unknown 2010 Katla lava dome Iceland Iceland hotspot Rhyolite 1999Eyjafjallajökull and Katla: restless neighbours Lassen Peak United States Cascade Volcanic Arc Dacite 1917 Black Butte (Siskiyou County, California) United States Cascade Volcanic Arc Dacite 9500 BP Bridge River Vent lava dome Canada Cascade Volcanic Arc Dacite ca. 300 BCLa Soufrière lava domeSaint Vincent and the GrenadinesLesser Antilles Volcanic Arc Andesite 2021 Mount Merapi lava dome Indonesia Sunda Arc Basaltic Andesite 2010 onwards Nea Kameni Greece South Aegean Volcanic Arc Dacite 1950 Novarupta lava dome United States Aleutian Arc Rhyolite 1912 Nevados de Chillán lava domes Chile Southern Volcanic Zone Dacite 1986 Puy de Dôme France Chaîne des Puys Potassic trachyte Santa María lava dome Guatemala Central America Volcanic Arc Dacite 2009 Sollipulli lava dome Chile Southern Volcanic Zone Andesite to Dacite 1240 ± 50 years Soufrière Hills lava dome Montserrat Lesser Antilles Andesite 2009 Mount St. Helens lava domes United States Cascade Volcanic Arc Dacite 2008 Torfajökull lava dome Iceland Iceland hotspot Rhyolite 1477 Tata Sabaya lava domes Bolivia Andes Andesite ~ Holocene Tate-iwa Japan Japan Arc Dacite Miocene Tatun lava domes Taiwan Andesite 648 Valles lava domes United States Jemez Mountains Rhyolite 50,000-60,000 BP Wizard Island lava dome United States Cascade Volcanic Arc High silica dacite to low silica rhyolite (rhyodacite)Map of Post-Caldera Volcanism and Crater Lake USGS Cascades Volcano Observatory. Retrieved 2014-01-31. 2850 BC
References
External links
Global Volcanism Program: Lava Domes USGS Photo glossary of volcano terms: Lava dome