The Crowsnest Formation , also called the Crowsnest Volcanics , is a geological formation in southwestern Alberta , Canada , on the southwestern margin of the Western Canada Sedimentary Basin . It was named for the Crowsnest Pass near Coleman, Alberta . The formation consists mostly of pyroclastic rocks that were laid down in a series of explosive eruptions about 100 million years ago during the Albian stage of the Early Cretaceous epoch. It contains unusual minerals such as melanite (a variety of andradite garnet ) and analcime (a variety of zeolite ).
21-453: The formation contains pyroclastic flows , lahars , agglomerates , tuffs and ash-fall deposits, as well as volcanic-rich sandstones and other sediments. The whole-rock chemistry of the volcanics is relatively normal, ranging from trachyandesite ( latite ) to phonolite and trachyte , but the mineralogy is unusual. In addition to analcime and melanite, common minerals include sanidine , aegerine - augite and chlorite . Blairmorite ,
42-587: A marine transgression in the Late Cretaceous . The volcanics were laid down on an inland floodplain that is represented by the underlying Ma Butte Formation. The eruptions probably occurred to the west near what is now Cranbrook, British Columbia , and the material was subsequently moved eastward by thrust faulting during the Laramide orogeny . It's estimated that the volcanics originally covered an area of about 1,800 km (690 sq mi), and their volume
63-454: A pyroclastic density current or a pyroclastic cloud ) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra ) that flows along the ground away from a volcano at average speeds of 100 km/h (30 m/s; 60 mph) but is capable of reaching speeds up to 700 km/h (190 m/s; 430 mph). The gases and tephra can reach temperatures of about 1,000 °C (1,800 °F). Pyroclastic flows are
84-425: A pyroclastic flow traveled for several hundreds of meters above the sea. A pyroclastic flow can interact with a body of water to form a large amount of mud, which can then continue to flow downhill as a lahar . This is one of several mechanisms that can create a lahar. In 1963, NASA astronomer Winifred Cameron proposed that the lunar equivalent of terrestrial pyroclastic flows may have formed sinuous rilles on
105-690: A rare analcime-rich rock-type named for the town of Blairmore, Alberta , is known only from the Crowsnest Formation and a locality in Mozambique . The Crowsnest Formation is the uppermost unit of the Blairmore Group . Exposures along the Crowsnest Highway ( Highway 3 ) and the railroad west of Coleman are the type locality . It is underlain by the Ma Butte Formation (also known as
126-438: A research team at Kiel University , Germany, of pyroclastic flows moving over the water. When the reconstructed pyroclastic flow (stream of mostly hot ash with varying densities) hit the water, two things happened: the heavier material fell into the water, precipitating out from the pyroclastic flow and into the liquid; the temperature of the ash caused the water to evaporate, propelling the pyroclastic flow (now only consisting of
147-448: Is a fluidised mass of turbulent gas and rock fragments that is ejected during some volcanic eruptions . It is similar to a pyroclastic flow but it has a lower density or contains a much higher ratio of gas to rock, which makes it more turbulent and allows it to rise over ridges and hills rather than always travel downhill as pyroclastic flows do. The speed of pyroclastic density currents has been measured directly via photography only in
168-496: Is estimated at 209 km (50 cu mi). The Crowsnest Volcanics are exposed along a series of folded, west-dipping fault plates in the Front Ranges and foothills of the southern Canadian Rockies . They reach maximum thicknesses of 426 to 488 metres (1,400 to 1,600 ft) along a trend that extends northward from Coleman along McGillivray Ridge to Ma Butte. Pyroclastic flow A pyroclastic flow (also known as
189-548: Is sometimes abbreviated to PDC (pyroclastic density current). Several mechanisms can produce a pyroclastic flow: Flow volumes range from a few hundred cubic meters to more than 1,000 cubic kilometres (240 cu mi). Larger flows can travel for hundreds of kilometres, although none on that scale has occurred for several hundred thousand years. Most pyroclastic flows are around one to ten cubic kilometres ( 1 ⁄ 4 – 2 + 1 ⁄ 2 cu mi) and travel for several kilometres. Flows usually consist of two parts:
210-524: The 1883 eruption of Krakatoa , supported by experimental evidence, shows that pyroclastic flows can cross significant bodies of water. However, that might be a pyroclastic surge , not flow, because the density of a gravity current means it cannot move across the surface of water. One flow reached the Sumatran coast as far as 48 kilometres (26 nautical miles) away. A 2006 BBC documentary film, Ten Things You Didn't Know About Volcanoes , demonstrated tests by
231-490: The Moon . In a lunar volcanic eruption, a pyroclastic cloud would follow local relief, resulting in an often sinuous track. The Moon's Schröter's Valley offers one example. Some volcanoes on Mars , such as Tyrrhenus Mons and Hadriacus Mons , have produced layered deposits that appear to be more easily eroded than lava flows, suggesting that they were emplaced by pyroclastic flows. Pyroclastic surge A pyroclastic surge
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#1732852216958252-536: The Taal Volcano eruption of 1965 in the Philippines, where a visiting volcanologist from USGS recognized the phenomenon as congruent to base surge in nuclear explosions . Very similar to the ground-hugging blasts associated with nuclear explosions, these surges are expanding rings of a turbulent mixture of fragments and gas that surge outward at the base of explosion columns. Base surges are more likely generated by
273-639: The basal flow hugs the ground and contains larger, coarse boulders and rock fragments, while an extremely hot ash plume lofts above it because of the turbulence between the flow and the overlying air, admixing and heating cold atmospheric air causing expansion and convection. Flows can deposit less than 1 meter to 200 meters in depth of loose rock fragment. The kinetic energy of the moving cloud will flatten trees and buildings in its path. The hot gases and high speed make them particularly lethal, as they will incinerate living organisms instantaneously or turn them into carbonized fossils: Testimonial evidence from
294-622: The Mill Creek Formation). The contact is gradational, with volcanic fragments becoming progressively more common toward the top of the Ma Butte Formation. The lower part of the formation is trachytic with abundant sanidine phenocrysts, melanite and pyroxene. The upper part contains sanidine, analcime, melanite and rock fragments. It is unconformably overlain by the shales of the Blackstone Formation that were deposited during
315-417: The boundary conditions separating convection from collapse. That is, switching rapidly from one condition to the other. These deposits are often found at the base of pyroclastic flows. They are thinly bedded, laminated and often cross-bedded. Typically they are about 1 m. thick and consist mostly of lithic and crystal fragments (fine ash elutriated away). They appear to form from the flow itself, but
336-513: The case of Mount St. Helens , where they reached 320-470 km/h, or 90–130 m/s (200–290 mph). Estimates of other modern eruptions are around 360 km/h, or 100 m/s (225 mph). Pyroclastic flows may generate surges. For example, the city of Saint-Pierre in Martinique in 1902 was overcome by one. Pyroclastic surge include 3 types, which are base surge, ash-cloud surge, and ground surge. Base surges were first recognized after
357-674: The dark is nuée ardente (French, "burning cloud"); this was notably used to describe the disastrous 1902 eruption of Mount Pelée on Martinique , a French island in the Caribbean. Pyroclastic flows that contain a much higher proportion of gas to rock are known as "fully dilute pyroclastic density currents" or pyroclastic surges . The lower density sometimes allows them to flow over higher topographic features or water such as ridges, hills, rivers, and seas. They may also contain steam, water, and rock at less than 250 °C (480 °F); these are called "cold" compared with other flows, although
378-534: The interaction of magma and water or phreatomagmatic eruptions . They develop from the interaction of magma (often basaltic) and water to form thin wedge-shaped deposits characteristic of maars . These are the most devastating. They form thin deposits, but travel at great speed (10–100 m/s) carrying abundant debris such as trees, rocks, bricks, tiles, etc. They are so powerful that they often blast and erode material (like sandblasting ). They are possibly produced when conditions in an eruption column are close to
399-485: The lighter material) along on a bed of steam at an even faster pace than before. During some phases of the Soufriere Hills volcano on Montserrat, pyroclastic flows were filmed about 1 km ( 1 ⁄ 2 nmi) offshore. These show the water boiling as the flow passes over it. The flows eventually built a delta, which covered about 1 km (250 acres). Another example was observed in 2019 at Stromboli when
420-539: The most deadly of all volcanic hazards and are produced as a result of certain explosive eruptions ; they normally touch the ground and hurtle downhill or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. The word pyroclast is derived from the Greek πῦρ ( pýr ), meaning "fire", and κλαστός ( klastós ), meaning "broken in pieces". A name for pyroclastic flows that glow red in
441-436: The temperature is still lethally high. Cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. Fronts of some pyroclastic density currents are fully dilute; for example, during the eruption of Mount Pelée in 1902, a fully dilute current overwhelmed the city of Saint-Pierre and killed nearly 30,000 people. A pyroclastic flow is a type of gravity current ; in scientific literature, it
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