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. 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 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). There is another prominent coulée flow on the flank of Llullaillaco volcano, in Argentina, and other examples in the Andes. Examples of lava domes References External links Global Volcanism Program: Lava Domes USGS Photo glossary of volcano terms: Lava dome Volcanic landforms