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30-491: True to its name, the glacier lies inside the north-facing crater left by the 1980 eruption of Mount St. Helens and the glacier's elevation is about 6,794 ft (2,071 m). A massive central lava dome emplaced from 1980 to 1987 occupies the center of the crater, and the glacier formed in the shape of a horseshoe around the dome, with two terminal moraines on the eastern and western sides. Heavy winter snowfall , repeated snow avalanches , rockfalls , and sun-shading by

60-418: A much lower rim on one side. Some volcanoes, such as maars , consist of a crater alone, with scarcely any mountain at all. These volcanic explosion craters are formed when magma rises through water-saturated rocks, which causes a phreatic eruption . Volcanic craters from phreatic eruptions often occur on plains away from other obvious volcanoes. Not all volcanoes form craters. Icefall An icefall

90-581: A very rapid advance of the glacier termini; first the western glacier arm merged with the rock glacier on the western crater wall and then, both arms of the Crater Glacier joined north 1980s lava dome in May 2008, despite the volcanic activity. In addition, the volcanic activity modified the surface of the glacier and transformed it from being mostly crevasse-free to being a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs due to movement of

120-402: A volcano's magma chamber may empty enough for an area above it to subside, forming a type of larger depression known as a caldera . In most volcanoes, the crater is situated at the top of a mountain formed from the erupted volcanic deposits such as lava flows and tephra . Volcanoes that terminate in such a summit crater are usually of a conical form. Other volcanic craters may be found on

150-445: Is a portion of certain glaciers characterized by relatively rapid flow and chaotic crevassed surface, caused in part by gravity. The term icefall is formed by analogy with the word waterfall , which is a similar phenomenon of the liquid phase but at a more spectacular speed. When ice movement of a glacier is faster than elsewhere, because the glacier bed steepens or narrows, and the flow cannot be accommodated by plastic deformation,

180-433: Is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions , molten magma and volcanic gases rise from an underground magma chamber , through a conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as lava . A volcanic crater can be of large dimensions, and sometimes of great depth. During certain types of explosive eruptions ,

210-480: The USGS Cascades Volcano Observatory strongly supported Crater Glacier, and also commented that Tulutson may not be an appropriate name since the volcano "lies inland in a region where the native language was not Cowlitz but Sahaptin ." After the decision, some controversy erupted following an editorial in a local newspaper protesting the decision, and the state of Washington "has indicated that

240-599: The United States. The name Tulutson Glacier was submitted for consideration, along with Crater Glacier and Kraffts Glacier, which would have honored the volcanologists Katia and Maurice Krafft , killed by a pyroclastic flow in 1991. In June 2006, the U.S. BGN chose Crater Glacier because of its two-decade precedent of common use, despite objections from the state of Washington and the United States Forest Service which both preferred Tulutson. The scientists at

270-406: The crater about seven to nine years later. However, the existence of the glacier was not publicized until 1999. By 2004, Crater Glacier covered about 0.36 square mile (0.93 km), about 20% of the glacier area in the pre-1980 glaciers, and there was a western and eastern lobe flowing around the 1980s dome. Due to the gas emissions on the crater floor, there were glacier caves ( ice caves ) in

300-470: The crater floor also reduced the amount of meltwater flowing out of the crater. After the volcanic activity of the 2000s, the thickness of the glacier continues to increase at a slower rate of 15 ft (5 m) per year and the glacier continues to advance at 3 ft (1 m) per day. The latest aerial imagery taken in 2012 shows that the glacier has entered the upper reaches of the Loowit Creek canyon and

330-415: The crater floor and lava dome growth. At the south end, the new domes almost split the Crater Glacier into two separate glaciers and melted 10% in volume of the glacier's ice. However, cold rock on the edge of the glacier insulated the glacier ice from the 1,300  °F (700  °C ) lava spewing out of the lava domes, easing concerns of a catastrophic lahar caused by glacier melting. The porous nature of

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360-434: The eruptions ceased in the winter of 1980, the crater floor cooled down enough for snow and ice accumulation. Beginning with snowfall in the winter of 1980-1981, the glacier began to grow very rapidly in the shadow of the crater. The glacier thickened at a rate of as high as 50 ft (15 m) per year and advanced northward as much as 135 ft (41 m) a year. This glacier growth was discovered by scientists working in

390-432: The flanks of volcanoes, and these are commonly referred to as flank craters . Some volcanic craters may fill either fully or partially with rain and/or melted snow, forming a crater lake . These lakes may become soda lakes , many of which are associated with active tectonic and volcanic zones. A crater may be breached during an eruption, either by explosions or by lava , or through later erosion. Breached craters have

420-460: The flow of ice in an icefall may be measured in kilometres per year. Such rapid flow cannot be accommodated by plastic deformation of the ice. Instead, the ice fractures, forming crevasses . Intersecting fractures form ice columns or seracs . These processes are imperceptible for the most part; however, a serac may collapse or topple abruptly and without warning. This behavior often poses the biggest risk to mountaineers climbing in an icefall. As

450-521: The glacier caves on the summit of Mount Rainier. Most of the glacier caves were located near the 1980s lava dome, where hot steam and volcanic gas emissions from hidden fumaroles on the crater floor or lava dome melted holes in the young glacial ice. About 7,900 feet or 2.4 km of caves and passageways in the glacier were mapped and studied. Since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice to Crater Glacier below. In addition, there are two rock glaciers to

480-455: The glacier transitions below the icefall, the topography of the glacier bed plays a crucial role in modifying its dynamics, leading to a flatter and/or wider bed that significantly reduces the velocity of ice movement. This change in speed and pressure causes crevasses to close up, resulting in a smoother glacier surface that presents fewer challenges for navigation and traversal. Icefalls vary greatly in height. The Roosevelt Glacier icefall, on

510-418: The glacier was first observed to be forming and actively flowing in the late 1980s, most scientists working on the mountain have referred to it informally as the "crater glacier". That name has been in wide use with the public (at least those who were aware of the glacier's existence) for the two decades since the glacier formed, and has appeared in several scientific publications too. A single scientific paper,

540-562: The glacier. At that time, a proponent from the Cowlitz tribe suggested the name "Tulutson Glacier," from the Cowlitz language word for ice. In March 2005, the Washington State Board on Geographic Names chose Tulutson over three other contenders (Crater, Spirit, and Tamanawas), and so Tulutson Glacier became the de facto name. However, the U.S. Board on Geographic Names had yet to make its decision, which would be official throughout

570-401: The headwaters of the creek. Ice mixed with rock debris now spills into the canyon and the creek has been pushed to the east. Nearby, on the slopes of the eastern crater wall, the glacier touches one of the rock glaciers and the glacier is very close to merging with the other rock glacier. A medial moraine can be seen at the interface of the eastern and western arms of the Crater Glacier. Since

600-438: The ice fractures, forming crevasses. Where two fractures meet, seracs (or ice towers) can be formed. When the movement of the ice slows down, the crevasses can coalesce, resulting in the surface of the glacier becoming smoother. Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/or narrows. Most glacier ice flows at speeds of a few hundred metres per year or less. However,

630-411: The most complete published study of the glacier to date, referred to it as the "Amphitheater glacier," but that name has not been used otherwise. Despite numerous observations and publications about the growing glacier in the late 1990s and early 2000s, no move was made to give the glacier a permanent and official name until late 2004, after the current eruptive cycle began and the new dome began to split

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660-453: The name Tulutson Glacier will continue to appear on State products, although if the feature melts soon, as is anticipated, this may not be a great concern." Despite these protests, the glacier's official name remained Crater Glacier, though shortly after their June 2006 decision, the BGN received a follow-up proposal to name the two arms of the glacier, East Crater Glacier and West Crater Glacier. This

690-412: The new glacier was about 40%-50% as large as all the pre–1980 glaciers combined. The surface of the glacier looks dark and dirty in the summer due to the numerous rockfalls from the steep, unstable crater walls along with ash from eruptions, all of which help to insulate and protect the growing glacier. The 2004-2008 volcanic activity created a series of domes that nearly split the glacier into two lobes at

720-422: The north face of Mount Baker ( Cascade Range , U.S.), is about 730 metres (2,400 feet) high. The ice cliff of the left side of the ice fall and above the debris covering the glacier is 20 to 40 metres (66 to 131 ft) high. Typical of mountain glaciers, this icefall forms as the ice flows from a high elevation plateau or basin accumulation zone to a lower valley ablation zone. Much larger icefalls may be found in

750-490: The north of the eastern lobe of Crater Glacier and one north of the western lobe. Two of these rock glaciers have merged with the Crater Glacier, with one on the west and one on the east. The other rock glacier on the eastern slopes of the crater wall is very close to touching the glacier. In the months after the eruption , the crater floor of St. Helens remained hot and unstable, with five minor volcanic eruptions , and lava dome construction between May and October 1980. After

780-423: The once smooth glacial ice, and several of them had been explored by the late 1990s. With the volcanic activity from 2004 to 2008, the glacier lobes were pushed aside and overthickened by the growth of new volcanic domes. As the two streams of ice were compressed between the crater wall and the new lava domes, the ice moved rapidly downhill, much like the squeezing of toothpaste out of a container. This resulted in

810-592: The outlet glaciers of continental ice sheets . The icefall feeding the Lambert Glacier in Antarctica is 7 kilometres (4.3 miles) wide and 14 kilometres (8.7 miles) long, even though the elevation difference is only 400 metres (1,300 feet), a little more than half that of the Roosevelt Glacier icefall. Icefalls are climbed because of their beauty and the challenge they pose. In some cases, an icefall may provide

840-485: The south end of the crater. In spite of the four-year lava dome building period, the glacier remains North America 's youngest and fastest growing glacier. With the joining of the termini on the north end of Crater Glacier in May 2008, the body of ice completely encircles the lava domes. Meltwater from the glacier gives rise to Loowit Creek . In 2000, glacier caves were discovered on the then-smooth glacier surface. Many of these glacier caves were big enough to explore, like

870-407: The surrounding cliffs to the south, led to the exceptionally rapid growth of this glacier. Thus, the glacier composition is estimated to be 60% ice and 40% rock, with an average thickness of 328 feet (100 m) and a maximum thickness of around 656 feet (200 m); nearly as deep as Mount Rainier 's Carbon Glacier . None of the ice is older than the year 1980, but by 2001 the volume of

900-404: Was because, at that point in time, the dome-building eruptions had nearly split the glacier into an east and west arm. No further action has been taken on this matter and the merging of the ice streams north of the 1980s lava dome has rendered this move unnecessary. Volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It

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