Geology 12 – Dalesandro Notes - Volcanoes (cont.) -A lava dome (also called a volcanic dome) is a mass of igneous rock formed when magma solidifies directly above a volcano’s vent. The dome swells in size as new magma comes up from below. If the pressure is not released somehow, the dome may eventually cause a massive explosion. -Plateau basalts are flat areas created when enormous flows of lava solidify. No modern volcanic eruption has produced enough lava to create a plateau basalt. Columnar jointing is a property exhibited by basalt as it cools. It forms what appear to be columns of rock (see figure 7.28B on page 198). -Submarine eruptions occur when a volcano erupts underwater. These eruptions can produce pillow basalt – strange-looking round blobs of rapidlycooled rock resembling pillows. -Volcanoes on earth occur on every continent, but are concentrated in two main areas: 1) The Circum-Pacific Belt (the “Ring of Fire”). This string of volcanoes circles the Pacific ocean. Most of the world’s famous volcanoes are found here, including Mt. St. Helens, Popocatepetl, Mt. Pinotubo, and El Chichon. 2) The Mediterranean Belt. This belt of volcanoes circles the Mediterranean Sea. Some notable volcanoes found here include Mt. Etna, Mt. Vesuvius, and Stromboli. -Some volcanoes do not fall into either of these two belt regions. Examples of these volcanoes include Kilauea in Hawaii, Mt. Erebus in Antarctica, and Surtsey in Iceland. -Five clues that a volcanic eruption may be imminent: 1) 2) 3) 4) 5) An increase in steam, ash, or pyroclastic material ejection. Increased seismic activity (earthquakes and tremors). Changes in the size or shape of the mountain (measured by lasers). Lava domes forming and/or increasing in size. Other geothermal activity including: New hot springs/geysers or increase in temperature in existing ones. Subterranean release of sulfur dioxide or carbon monoxide gas, possibly killing wildlife. Increased acidity of lakes, ponds, and rivers.