Lahar in the context of "Volcanic lake"

Mount Pinatubo is an active stratovolcano in the Zambales Mountains in Luzon in the Philippines. Located on the tripoint of Zambales, Tarlac and Pampanga provinces, most people were unaware of its eruptive history before the pre-eruption volcanic activity in early 1991. Dense forests, which supported a population of several thousand indigenous Aetas, heavily eroded and obscured Pinatubo.

Pinatubo is known for its VEI-6 eruption on June 15, 1991, the second-largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in Alaska. The eruption coincided with Typhoon Yunya making landfall in the Philippines, which brought a dangerous mix of ash and rain to nearby towns and cities. Early predictions led to the evacuation of tens of thousands of people, saving many lives. The eruption severely damaged surrounding areas with pyroclastic surges, pyroclastic falls, and later, flooding lahars caused by rainwater re-mobilizing volcanic deposits. This destruction affected infrastructure and altered river systems for years. Minor dome-forming eruptions inside the caldera continued from 1992 to 1993.

Meltwater (or melt water) is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found during early spring when snow packs and frozen rivers melt with rising temperatures, and in the ablation zone of glaciers where the rate of snow cover is reducing. Meltwater can be produced during volcanic eruptions, in a similar way in which the more dangerous lahars form. It can also be produced by the heat generated by the flow itself.

When meltwater pools on the surface rather than flowing, it forms melt ponds. As the weather gets colder, meltwater will often re-freeze. Meltwater can also collect or melt under the ice's surface. These pools of water, known as subglacial lakes, can form due to geothermal heat and friction. Melt ponds may also form above and below Arctic sea ice, decreasing its albedo and causing the formation of thin underwater ice layers or false bottoms.

Petrified wood (from Ancient Greek πέτρα meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.

The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls act as a template for mineralization. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. Most of the organic matter often decomposes, however some of the lignin may remain. Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. However, petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. A forest where such material has petrified becomes known as a petrified forest.

Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it was deposited in, or whether nonvolcanic material is mingled with the volcanic clasts. The United States Geological Survey defines volcaniclastics somewhat more narrowly, to include only rock composed of volcanic rock fragments that have been transported some distance from their place of origin.

In the broad sense of the term, volcaniclastics includes pyroclastic rocks such as the Bandelier Tuff; cinder cones and other tephra deposits; the basal and capping breccia that characterize ʻaʻā lava flows; and lahars and debris flows of volcanic origin.

Mount Rainier (/reɪ.ˈnɪər/ ray-NEER), also known as Tahoma, is a large active stratovolcano in the Cascade Range of the Pacific Northwest in the United States. The mountain is located in Mount Rainier National Park about 59 miles (95 km) south-southeast of Seattle. At around 14,000 feet (4,400 m) it is the highest mountain in the U.S. state of Washington, the most topographically prominent mountain in the contiguous United States, and the tallest in the Cascade Volcanic Arc.

Due to its high probability of an eruption in the near future and proximity to a major urban area, Mount Rainier is considered one of the most dangerous volcanoes in the world, and it is on the Decade Volcano list. The large amount of glacial ice means that Mount Rainier could produce massive lahars that could threaten the entire Puyallup River valley and other river valleys draining Mount Rainier, including the Carbon, White, Nisqually, and Cowlitz (above Riffe Lake). According to the United States Geological Survey's 2008 report, "about 80,000 people and their homes are at risk in Mount Rainier's lahar-hazard zones."

Augustine Volcano (Sugpiaq: Utakineq; Dena'ina: Chu Nula) is a stratovolcano in Alaska consisting of a central complex of summit lava domes and flows surrounded by an apron of pyroclastic, lahar, avalanche, and ash deposits. The volcano forms Augustine Island, colloquially called Mount St. Augustine, in southwestern Cook Inlet in the Kenai Peninsula Borough of southcentral coastal Alaska, about 70 miles (113 km) west of Homer and about 175 miles (282 km) southwest of Anchorage.

The volcano is frequently active, with major eruptions recorded in 1883, 1935, 1963–64, 1976, 1986, and 2006. Minor eruptive events were reported in 1812, 1885, 1908, 1944, and 1971. The large eruptions are characterized by an explosive onset followed by the quieter effusion of lava. Augustine Island has a land area of 32.4 square miles (83.9 km), while West Island, just off Augustine's western shores, has 2 sq mi (5.2 km). The irregular coastline of Augustine Island is due to the repeated catastrophic collapse of the summit dome, forming debris avalanches down the flanks and into Cook Inlet.

Most non-water floods (excluding mudflows, oil spills, or volcanic lahars) involve storage facilities suddenly releasing liquids, or industrial retaining reservoirs releasing toxic waste. Storage facility incidents usually cover a small area but can be catastrophic in cities. For example, a molasses tank failure in 1919 led to the Great Molasses Flood that killed 21 people in Boston, Massachusetts, U.S.

Industrial retaining reservoirs are often used to store toxic waste, and when they fail they can flood a large area, causing physical and environmental damage. The 2010 failure of a reservoir at the Ajka alumina plant in Hungary flooded a small town and killed several, while the cleanup from the 2008 Kingston Fossil Plant spill in Tennessee, U.S. took several years and killed at least 40 workers involved.

In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated for nearly two months until a catastrophic, major explosive eruption took place on May 18, 1980, at 8:32 a.m. The eruption, which had a volcanic explosivity index of 5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California. It has often been considered the most disastrous volcanic eruption in U.S. history.

The eruption was preceded by a series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:11 am PDT (UTC−7) on May 18, 1980, caused the entire weakened north face to slide away, a sector collapse which was the largest subaerial landslide in recorded history. This allowed the partly molten rock, rich in high-pressure gas and steam, to suddenly explode northward toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the landslide. An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in eleven U.S. states and various Canadian provinces. At the same time, snow, ice, and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles (80 km; 260,000 ft) to the southwest. Less severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later that year. The thermal energy released during the eruption was equal to 26 megatons of TNT.