Lava dome

Image of the rhyolitic lava dome of Chaitén Volcano during its 2008–2009 eruption.

One of the Mono Craters, an example of a rhyolite dome.

Lava domes in the crater of Mount St. Helens

In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. The geochemistry of lava domes can vary from basalt to rhyolite although most preserved domes tend to have high silica content. 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 consists of rhyolite or dacite.

Dome dynamics

Lava domes are dynamic structures that evolve over time undergoing various processes such as growth, collapse, solidification and erosion.

Lava domes grow by endogenic dome growth or exogenic dome growth. The first one implies dome interior expansion to accommodate new lava and the second one refers to superficial piling up of lava. 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. 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 build up of gas pressure, erupting domes can often experience episodes of explosive eruption over time. If part of a lava dome collapses while it is still molten, it can produce pyroclastic flows, one of the most lethal forms of volcanic event. Other hazards associated with lava domes are the destruction of property, forest fires, and lahars triggered by pyroclastic flows near mud, snow and ice. Lava domes are one of the principal structural features of many stratovolcanoes worldwide. Lava domes cause explosions to become more dangerous since they 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.

Related landforms

Cryptodomes

Photo showing the bulging cryptodome of Mt. St. Helens on April 27, 1980.

A cryptodome (from Greek κρυπτός, kryptos, "hidden, secret") is a dome-shaped structure created by accumulation of viscous magma at a shallow depth. One example of a cryptodome was in the May 1980 eruption of Mount St. Helens, where the explosive eruption began after a landslide caused the side of the volcano to fall, leading to explosive decompression of the subterranean cryptodome.

Lava coulees

Coulees are lava domes that have experienced some flow away from their original position, thus resembling both lava domes and lava flows.

Examples of lava domes

Main article: List of lava domes

Lava domes

Dome or volcano name	Country	Volcanic area	Composition	Last dome eruption or growth episode
Chaitén	Chile	Southern Volcanic Zone	Rhyolite	2009
Cordón Caulle	Chile	Southern Volcanic Zone	Rhyodacite to Rhyolite	Holocene
Galeras	Colombia	Northern Volcanic Zone
Katla	Iceland	Iceland hotspot	Rhyolite	1999 onwards
Lassen Peak	California, USA	Cascade Volcanic Arc	Basalt	1917
Mount Meager	British Columbia, Canada	Cascade Volcanic Arc	Dacite	2350 BP
Mount Merapi	Indonesia	Sunda Arc
Nea Kameni	Greece
Volcán Nuevo	Chile	Southern Volcanic Zone	Dacite	1986
Puy-de-Dôme	France	Chaîne des Puys		ca. 5760 BC
Santiaguito	Guatemala	Central America Volcanic Arc	Dacite	2009
Sollipulli	Chile	Southern Volcanic Zone	Andesite to Dacite
Soufrière Hills	Montserrat	Lesser Antilles		2009
Mount St. Helens	Washington, USA	Cascade Volcanic Arc	Basalt	2008
Torfajökull	Iceland	Iceland hotspot	Rhyolite
Unnamed	Japan	Japan Arc	Dacite	Miocene
Wizard Island	Oregon, USA	Cascade Volcanic Arc	Basalt	2850 BC

References

• Global Volcanism Program: Lava Domes
• USGS Photo glossary of volcano terms: Lava dome
• Sparks, R.S.J. (August 1997), "Causes and consequences of pressurisation in lava dome eruptions", Earth and Planetary Science Letters 150 (3–4): 177–189, Bibcode 1997E&PSL.150..177S, doi:10.1016/S0012-821X(97)00109-X, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4177RWJ-1&_user=778111&_coverDate=08%2F31%2F1997&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000043085&_version=1&_urlVersion=0&_userid=778111&md5=c0def50303a799fcb146e880c79fb89d 
• 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, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VCS-48B0RF7-2W&_user=778111&_coverDate=09%2F30%2F1983&_fmt=abstract&_orig=search&_cdi=5962&view=c&_acct=C000043085&_version=1&_urlVersion=0&_userid=778111&md5=8da52641a1e571b220630bba6cf622f3&ref=full