A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The process that forms volcanoes is called volcanism.
Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.
Popocatépetl is an active stratovolcano located in the states of Puebla, Morelos, and Mexico in central Mexico. It lies in the eastern half of the Trans-Mexican Volcanic Belt. At 5,393 m (17,694 ft) it is the second highest peak in Mexico, after Citlaltépetl at 5,636 m (18,491 ft).
A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica, with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi).
A volcanologist, or volcano scientist, is a geologist who focuses on understanding the formation and eruptive activity of volcanoes. Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions, collect eruptive products including tephra, rock and lava samples. One major focus of inquiry in recent times is the prediction of eruptions to alleviate the impact on surrounding populations and monitor natural hazards associated with volcanic activity. Geologists who research volcanic materials that make up the solid Earth are referred to as igneous petrologists.
Pneumonoultramicroscopicsilicovolcanoconiosis is a 45-letter word coined in 1935 by the then-president of the National Puzzlers' League, Everett M. Smith. It has sometimes been used as a synonym for the occupational disease known as silicosis, but it should not be as most silicosis is not related to mining of volcanic dusts. It is the longest word in the English language published in a popular dictionary, Oxford Dictionaries, which defines it as "an artificial long word said to mean a lung disease caused by inhaling very fine ash and sand dust".
Vog is a form of air pollution that results when sulfur dioxide and other gases and particles emitted by an erupting volcano react with oxygen and moisture in the presence of sunlight. The word is a portmanteau of the words "volcanic" and "smog". The term is in common use in the Hawaiian Islands, where the Kīlauea volcano, on the Island of Hawaiʻi (the "Big Island"), erupted continuously between 1983 and 2018. Based on June 2008 measurements, Kīlauea emits 2,000–4,000 tons of sulfur dioxide (SO2) every day.
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 to rhyolite although the majority are of intermediate composition 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.
Anak Krakatau is a volcanic island in Indonesia. On 29 December 1927, Anak Krakatau first emerged from the caldera formed in 1883 by the explosive volcanic eruption that destroyed the island of Krakatoa. There has been sporadic eruptive activity at the site since the late 20th century, culminating in a large underwater collapse of the volcano, which caused a deadly tsunami in December 2018. There has been subsequent activity since. Owing to its young age the island is one of several in the area that are of interest to, and the subject of extensive study by volcanologists.
Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through groundwater heated by volcanic action.
The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera circa 1600 BCE. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on nearby islands and the coast of Crete with subsequent earthquakes and paleotsunamis. With a Volcanic Explosivity Index (VEI) of 7, it resulted in the ejection of approximately 28–41 km3 (6.7–9.8 cu mi) of dense-rock equivalent (DRE), the eruption was one of the largest volcanic events in human history. Since tephra from the Minoan eruption serves as a marker horizon in nearly all archaeological sites in the Eastern Mediterranean, its precise date is of high importance and has been fiercely debated among archaeologists and volcanologists for decades, without coming to a definite conclusion.
The Mount Meager massif is a group of volcanic peaks in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located 150 km (93 mi) north of Vancouver at the northern end of the Pemberton Valley and reaches a maximum elevation of 2,680 m (8,790 ft). The massif is capped by several eroded volcanic edifices, including lava domes, volcanic plugs and overlapping piles of lava flows; these form at least six major summits including Mount Meager which is the second highest of the massif.
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C. The volcanic rock resulting from subsequent cooling is also often called lava.
A volcanic hazard is the probability a volcanic eruption or related geophysical event will occur in a given geographic area and within a specified window of time. The risk that can be associated with a volcanic hazard depends on the proximity and vulnerability of an asset or a population of people near to where a volcanic event might occur.
The International Volcanic Health Hazard Network (IVHHN) is an organization that provides research and information on the health hazards and impacts of volcanic eruptions. IVHHN work covers a range of research areas including volcanology, toxicology, public health and exposure science, with the goal of determining the health impacts of volcanic emissions and how to protect exposed communities.
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products, including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the gases shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometres away.
Sabancaya is an active 5,976-metre-high (19,606 ft) stratovolcano in the Andes of southern Peru, about 70 kilometres (43 mi) northwest of Arequipa. It is considered part of the Central Volcanic Zone of the Andes, one of the three distinct volcanic belts of the Andes. The Central Volcanic Zone includes a number of volcanoes, some of which like Huaynaputina have had large eruptions and others such as Sabancaya and Ubinas have been active in historical time. Sabancaya forms a volcanic complex together with Hualca Hualca to the north and Ampato to the south and has erupted andesite and dacite. It is covered by a small ice cap which leads to a risk of lahars during eruptions.
Tamsin Alice Mather is a British Professor of Earth Sciences at the Department of Earth Sciences, University of Oxford and a Fellow of University College, Oxford. She studies volcanic processes and their impacts on the Earth's environment and has appeared on the television and radio.
Susan Loughlin MBE is a British volcanologist. She was Director of the Montserrat Volcano Observatory from 2004-2006, and has been Head of Volcanology for the British Geological Survey since 2008.
