Misplaced Pages

#76923

100-654: Mount Berlin is a glacier -covered volcano in Marie Byrd Land , Antarctica , 100 kilometres (62 mi) from the Amundsen Sea . It is a roughly 20-kilometre-wide (12 mi) mountain with parasitic vents that consists of two coalesced volcanoes: Berlin proper with the 2-kilometre-wide (1.2 mi) Berlin Crater and Merrem Peak with a 2.5-by-1-kilometre-wide (1.55 mi × 0.62 mi) crater, 3.5 kilometres (2.2 mi) away from Berlin. The summit of

200-424: A cirque landform (alternatively known as a corrie or as a cwm ) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes ) – which collects and compresses through gravity the snow that falls into it. This snow accumulates and the weight of the snow falling above compacts it, forming névé (granular snow). Further crushing of the individual snowflakes and squeezing

300-834: A trachyte suite, which features both comendite and pantellerite . Phonolite is less common. Mafic rocks have been reported from flank vents, basanite and hawaiite from Mefford Knoll, benmoreite from the southeastern flank at Wedemeyer Rocks, phonotephrite from Brandenberger Bluff, and mugearite without any particular locality. Phenocrysts make up only a small portion of the volume and consist mostly of alkali feldspar , with subordinate apatite , fayalite , hedenbergite and opaque minerals. Benmoreite has more phenocrysts, which include anorthoclase , magnetite , olivine , plagioclase , pyroxene and titanaugite . Groundmass include basanite , mafic rocks, trachyte and trachy-phonolite . Xenoliths are also recorded. The magma erupted from Mount Berlin appears to have originated in

400-404: A volcanic vent located in a lake , coastal zone, marsh or an area of abundant groundwater . Tuff cones are steep sloped and cone shaped. They have wide craters and are formed of highly altered, thickly bedded tephra. They are considered to be a taller variant of a tuff ring, formed by less powerful eruptions. Tuff cones are usually small in height. Koko Crater is 1,208 feet. Santorini

500-571: A 227 CE eruption. The date of the last eruption of Mount Berlin is unclear but the Global Volcanism Program gives a date of 10,300±5,300 BP. Because of its Holocene activity, the volcano is considered active and several volcano tectonic earthquakes have been recorded on Mount Berlin. Mount Berlin is geothermally active, the only volcano in Marie Byrd Land with such activity. Steaming ice towers are found on

600-466: A Cretaceous erosion surface on which volcanoes rest. The volcanic activity at Mount Berlin may ultimately relate to the presence of a mantle plume that is impinging onto the crust in Marie Byrd Land. Two pyroclastic fallout deposits crop out in the crater rim, reaching thicknesses of 150 metres (490 ft). Other outcrops of fallout deposits occur at Merrem Peak. The Mount Berlin deposits reach thicknesses of more than 70 metres (230 ft) close to

700-522: A glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area is snow-covered at the end of the melt season, and they have a terminus with a vigorous flow. Following the Little Ice Age 's end around 1850, glaciers around the Earth have retreated substantially . A slight cooling led to

800-601: A glacier may flow into a body of water, it forms only on land and is distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water. On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions , but glaciers may be found in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand . Between latitudes 35°N and 35°S, glaciers occur only in

900-411: A glacier via moulins . Streams within or beneath a glacier flow in englacial or sub-glacial tunnels. These tunnels sometimes reemerge at the glacier's surface. Most of the important processes controlling glacial motion occur in the ice-bed contact—even though it is only a few meters thick. The bed's temperature, roughness and softness define basal shear stress, which in turn defines whether movement of

1000-408: A kilometer per year. Eventually, the ice will be surging fast enough that it begins to thin, as accumulation cannot keep up with the transport. This thinning will increase the conductive heat loss, slowing the glacier and causing freezing. This freezing will slow the glacier further, often until it is stationary, whence the cycle can begin again. The flow of water under the glacial surface can have

1100-404: A large effect on the motion of the glacier itself. Subglacial lakes contain significant amounts of water, which can move fast: cubic kilometers can be transported between lakes over the course of a couple of years. This motion is thought to occur in two main modes: pipe flow involves liquid water moving through pipe-like conduits, like a sub-glacial river; sheet flow involves motion of water in

SECTION 10

#1732801051077

1200-442: A length of about 20 kilometres (12 mi). Its slopes have inclinations of about 12–13°. The volcano is covered by glaciers , resulting in only a few rocky outcrops being visible on the mountain. Despite this, the volcano is considered to be well-exposed in comparison to other volcanoes in the region. Monogenetic volcanoes on the northern flank of Mount Berlin have generated two outcrops of mafic lava and scoria , one of which

1300-460: A lower heat conductance, meaning that the basal temperature is also likely to be higher. Bed temperature tends to vary in a cyclic fashion. A cool bed has a high strength, reducing the speed of the glacier. This increases the rate of accumulation, since newly fallen snow is not transported away. Consequently, the glacier thickens, with three consequences: firstly, the bed is better insulated, allowing greater retention of geothermal heat. Secondly,

1400-618: A south-southeast direction. Eruptions of Berlin include both effusive eruptions , that emplaced cinder cones and lava flows , and intense explosive eruptions ( Plinian eruptions ) which generated eruption columns up to 40 kilometres (25 mi) high. Such eruptions would have injected tephra into the stratosphere and deposited it across the southern Pacific Ocean and the West Antarctic Ice Sheet . The patterns of tephra deposition indicate that westerly winds transported tephra from Mount Berlin over Antarctica. During

1500-488: A thin layer. A switch between the two flow conditions may be associated with surging behavior. Indeed, the loss of sub-glacial water supply has been linked with the shut-down of ice movement in the Kamb ice stream. The subglacial motion of water is expressed in the surface topography of ice sheets, which slump down into vacated subglacial lakes. The speed of glacial displacement is partly determined by friction . Friction makes

1600-410: A tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by climate change than other glaciers. Thermally, a temperate glacier is at a melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing threshold from the surface to its base, although

1700-461: Is a major factor for identification in the field. Accretionary lapilli form as a result of the cohesive properties of wet ash, causing the particles to bind. They have a circular structure when specimens are viewed in hand and under the microscope . A further control on the morphology and characteristics of a deposit is the water to magma ratio. It is considered that the products of phreatomagmatic eruptions are fine grained and poorly sorted where

1800-468: Is a persistent body of dense ice that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries . It acquires distinguishing features, such as crevasses and seracs , as it slowly flows and deforms under stresses induced by its weight. As it moves, it abrades rock and debris from its substrate to create landforms such as cirques , moraines , or fjords . Although

1900-407: Is about 3,000 metres (9,800 ft) high and has a 2.5-by-1-kilometre-wide (1.55 mi × 0.62 mi) crater at its summit. These craters are aligned east–west, like other Flood Range calderas . Mount Berlin has variously been described as a composite volcano , shield volcano or stratovolcano with a volume of about 200 cubic kilometres (48 cu mi). The entire combined edifice has

2000-456: Is above or at freezing at the interface and is able to slide at this contact. This contrast is thought to a large extent to govern the ability of a glacier to effectively erode its bed , as sliding ice promotes plucking at rock from the surface below. Glaciers which are partly cold-based and partly warm-based are known as polythermal . Glaciers form where the accumulation of snow and ice exceeds ablation . A glacier usually originates from

2100-407: Is affected by factors such as slope, ice thickness, snowfall, longitudinal confinement, basal temperature, meltwater production, and bed hardness. A few glaciers have periods of very rapid advancement called surges . These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous movement state. These surges may be caused by the failure of the underlying bedrock,

SECTION 20

#1732801051077

2200-531: Is at least 492,000 years old and thus the oldest ice of West Antarctica. Dusty layers in ice cores have also been linked to Mount Berlin and other volcanoes in Antarctica. Among eruptions recorded at Mount Berlin are: Several tephra layers between 18,100 and 55,400 years old, found in Siple Dome ice cores, resemble those of Mount Berlin, as do tephras emplaced 9,346 and 2,067 BCE (interval 3.0 years) in

2300-411: Is because these peaks are located near or in the hyperarid Atacama Desert . Glaciers erode terrain through two principal processes: plucking and abrasion . As glaciers flow over bedrock, they soften and lift blocks of rock into the ice. This process, called plucking, is caused by subglacial water that penetrates fractures in the bedrock and subsequently freezes and expands. This expansion causes

2400-406: Is by basal sliding, where meltwater forms between the ice and the bed itself. Whether a bed is hard or soft depends on the porosity and pore pressure; higher porosity decreases the sediment strength (thus increases the shear stress τ B ). Porosity may vary through a range of methods. Bed softness may vary in space or time, and changes dramatically from glacier to glacier. An important factor

2500-434: Is called glaciology . Glaciers are important components of the global cryosphere . Glaciers are categorized by their morphology, thermal characteristics, and behavior. Alpine glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier , or alternatively, an alpine glacier or mountain glacier . A large body of glacial ice astride a mountain, mountain range, or volcano

2600-416: Is called rock flour and is made up of rock grains between 0.002 and 0.00625 mm in size. Abrasion leads to steeper valley walls and mountain slopes in alpine settings, which can cause avalanches and rock slides, which add even more material to the glacier. Glacial abrasion is commonly characterized by glacial striations . Glaciers produce these when they contain large boulders that carve long scratches in

2700-422: Is expected that tuff rings and tuff cones might be present on the surface of Mars . Tuff rings have a low profile apron of tephra surrounding a wide crater (called a maar crater) that is generally lower than the surrounding topography. The tephra is often unaltered and thinly bedded, and is generally considered to be an ignimbrite , or the product of a pyroclastic density current. They are built around

2800-504: Is extremely slow in the region. Volcanic activity appears to take place in three phases, an early mafic phase, often followed by a second felsic phase. End-stage volcanism occurs in the form of small cone-forming eruptions. Ignimbrites are rare in Marie Byrd Land; the outcrop on the southeastern flank of Mount Berlin is an uncommon exception. Activity in the Marie Byrd Land Volcanic Province began during

2900-488: Is found at Mefford Knoll on a linear vent. On the southeastern flank, a fiamme -rich ignimbrite crops out and is correlated to a flank vent on the northeastern flank. A ridge extends northwestward from Merrem Peak; at its foot is Brandenberger Bluff , a 300-metre-high (980 ft) outcrop of lava and tuff. This structure formed phreatomagmatically ; it was formerly interpreted as a subglacial hyaloclastite . Other topographical locations on Mount Berlin are Fields Peak on

3000-405: Is high enough to inhibit vesiculation in basaltic magma. Hyalo tuff is a type of rock formed by the explosive fragmentation of glass during phreatomagmatic eruptions at shallow water depths (or within aquifers ). Hyalotuffs have a layered nature that is considered to be a result of dampened oscillation in discharge rate, with a period of several minutes. The deposits are much finer grained than

3100-588: Is higher, and the mountains above 5,000 m (16,400 ft) usually have permanent snow. Even at high latitudes, glacier formation is not inevitable. Areas of the Arctic , such as Banks Island , and the McMurdo Dry Valleys in Antarctica are considered polar deserts where glaciers cannot form because they receive little snowfall despite the bitter cold. Cold air, unlike warm air, is unable to transport much water vapor. Even during glacial periods of

Mount Berlin - Misplaced Pages Continue

3200-513: Is part of the Southern Aegean volcanic arc , 140 km north of Crete . The Minoan eruption of Santorini, was the latest eruption and occurred in the first half of the 17th century BC. The eruption was of predominantly rhyodacite composition. The Minoan eruption had four phases. Phase 1 was a white to pink pumice fallout with dispersal axis trending ESE. The deposit has a maximum thickness of 6 m and ash flow layers are interbedded at

3300-519: Is recorded in outcrops on the volcano, in a blue-ice area on Mount Moulton , 30 kilometres (19 mi) away, at Mount Waesche, in ice cores and in marine sediment cores from the Southern Ocean . Several tephra layers found in ice cores all across Antarctica have been attributed to West Antarctic volcanoes and in particular to Mount Berlin. Tephras deposited by this volcano have been used to date ice cores, establishing that ice at Mount Moulton

3400-897: Is termed an ice cap or ice field . Ice caps have an area less than 50,000 km (19,000 sq mi) by definition. Glacial bodies larger than 50,000 km (19,000 sq mi) are called ice sheets or continental glaciers . Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of freshwater, enough that if both melted, global sea levels would rise by over 70 m (230 ft). Portions of an ice sheet or cap that extend into water are called ice shelves ; they tend to be thin with limited slopes and reduced velocities. Narrow, fast-moving sections of an ice sheet are called ice streams . In Antarctica, many ice streams drain into large ice shelves . Some drain directly into

3500-413: Is the region where there is a net loss in glacier mass. The upper part of a glacier, where accumulation exceeds ablation, is called the accumulation zone . The equilibrium line separates the ablation zone and the accumulation zone; it is the contour where the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. In general, the accumulation zone accounts for 60–70% of

3600-580: Is the theory of explosive thermal contraction of particles under rapid cooling from contact with water. In many cases the water is supplied by the sea, such as in the Surtsey eruption. In other cases the water may be present in a lake or caldera -lake, as at Santorini , where the phreatomagmatic component of the Minoan eruption was a result of both a lake and later the sea. There have also been examples of interaction between magma and water in an aquifer. Many of

3700-402: Is the underlying geology; glacial speeds tend to differ more when they change bedrock than when the gradient changes. Further, bed roughness can also act to slow glacial motion. The roughness of the bed is a measure of how many boulders and obstacles protrude into the overlying ice. Ice flows around these obstacles by melting under the high pressure on their stoss side ; the resultant meltwater

3800-552: Is then forced into the cavity arising in their lee side , where it re-freezes. As well as affecting the sediment stress, fluid pressure (p w ) can affect the friction between the glacier and the bed. High fluid pressure provides a buoyancy force upwards on the glacier, reducing the friction at its base. The fluid pressure is compared to the ice overburden pressure, p i , given by ρgh. Under fast-flowing ice streams, these two pressures will be approximately equal, with an effective pressure (p i – p w ) of 30 kPa; i.e. all of

3900-993: The Andes , the Himalayas , the Rocky Mountains , the Caucasus , Scandinavian Mountains , and the Alps . Snezhnika glacier in Pirin Mountain, Bulgaria with a latitude of 41°46′09″ N is the southernmost glacial mass in Europe. Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period . In New Guinea, small, rapidly diminishing, glaciers are located on Puncak Jaya . Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya , and in

4000-644: The Faroe and Crozet Islands were completely glaciated. The permanent snow cover necessary for glacier formation is affected by factors such as the degree of slope on the land, amount of snowfall and the winds. Glaciers can be found in all latitudes except from 20° to 27° north and south of the equator where the presence of the descending limb of the Hadley circulation lowers precipitation so much that with high insolation snow lines reach above 6,500 m (21,330 ft). Between 19˚N and 19˚S, however, precipitation

4100-760: The Himalayas , Andes , and a few high mountains in East Africa, Mexico, New Guinea and on Zard-Kuh in Iran. With more than 7,000 known glaciers, Pakistan has more glacial ice than any other country outside the polar regions. Glaciers cover about 10% of Earth's land surface. Continental glaciers cover nearly 13 million km (5 million sq mi) or about 98% of Antarctica 's 13.2 million km (5.1 million sq mi), with an average thickness of ice 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers. The volume of glaciers, not including

Mount Berlin - Misplaced Pages Continue

4200-575: The Hobbs Coast of the Amundsen Sea . The volcano was studied during field trips in December 1940, November 1967, November–December 1977 and 1994–1995. It is named after Leonard M. Berlin, who led the 1940 research visit to the mountain. Mount Berlin reaches a height of 3,478 metres (11,411 ft) above sea level, making it the highest volcano in the Flood Range . It is the western end of

4300-562: The Quaternary , Manchuria , lowland Siberia , and central and northern Alaska , though extraordinarily cold, had such light snowfall that glaciers could not form. In addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high (4,500 to 6,900 m or 14,800 to 22,600 ft) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This

4400-535: The Rwenzori Mountains . Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and Jan Mayen to the far north, New Zealand and the subantarctic islands of Marion , Heard , Grande Terre (Kerguelen) and Bouvet . During glacial periods of the Quaternary, Taiwan , Hawaii on Mauna Kea and Tenerife also had large alpine glaciers, while

4500-416: The cinder cones on Tenerife are considered to be phreatomagmatic because of these circumstances. The other competing theory is based on fuel-coolant reactions, which have been modeled for nuclear reactors. Under this theory, the fuel (in this case, the magma) fragments upon contact with a coolant (the sea, a lake or aquifer). The propagating stress waves and thermal contraction widen cracks and increase

4600-448: The 1990s and 2000s. In a study using data from January 1993 through October 2005, more events were detected every year since 2002, and twice as many events were recorded in 2005 as there were in any other year. Ogives or Forbes bands are alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces. They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals

4700-590: The Siple Dome A ice core. The marine "Tephra B" and "Tephra C" layers may also come from Mount Berlin but statistical methods have not supported such a relationship at least for "Tephra B". A 694±7 before present tephra layer found in the TALDICE ice core in East Antarctica may come from Mount Berlin or from Mount Melbourne and may have been erupted at the same time as an eruption of The Pleiades . Roosevelt Island has yielded glass shards that may come from

4800-412: The advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous. Glaciers move downhill by the force of gravity and the internal deformation of ice. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between layers. When the amount of strain (deformation) is proportional to

4900-520: The air from the snow turns it into "glacial ice". This glacial ice will fill the cirque until it "overflows" through a geological weakness or vacancy, such as a gap between two mountains. When the mass of snow and ice reaches sufficient thickness, it begins to move by a combination of surface slope, gravity, and pressure. On steeper slopes, this can occur with as little as 15 m (49 ft) of snow-ice. In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn . Under

5000-430: The amount of melting at surface of the glacier, the faster the ice will flow. Basal sliding is dominant in temperate or warm-based glaciers. The presence of basal meltwater depends on both bed temperature and other factors. For instance, the melting point of water decreases under pressure, meaning that water melts at a lower temperature under thicker glaciers. This acts as a "double whammy", because thicker glaciers have

5100-713: The annual movement of the glacier. Ogives are formed when ice from an icefall is severely broken up, increasing ablation surface area during summer. This creates a swale and space for snow accumulation in the winter, which in turn creates a ridge. Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives. Glaciers are present on every continent and in approximately fifty countries, excluding those (Australia, South Africa) that have glaciers only on distant subantarctic island territories. Extensive glaciers are found in Antarctica, Argentina, Chile, Canada, Pakistan, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in

SECTION 50

#1732801051077

5200-501: The basis of aerophysical surveys. The volcanic province is related to the West Antarctic Rift which is interpreted as a rift or as a plate boundary . The West Antarctic Rift has been volcanically and tectonically active over the past 30–25 million years. The basement crops out near the coast and consists of Paleozoic rocks with intruded Cretaceous and Devonian granites which were flattened by erosion, leaving

5300-432: The bedrock has frequent fractures on the surface, glacial erosion rates tend to increase as plucking is the main erosive force on the surface; when the bedrock has wide gaps between sporadic fractures, however, abrasion tends to be the dominant erosive form and glacial erosion rates become slow. Glaciers in lower latitudes tend to be much more erosive than glaciers in higher latitudes, because they have more meltwater reaching

5400-445: The bedrock. By mapping the direction of the striations, researchers can determine the direction of the glacier's movement. Similar to striations are chatter marks , lines of crescent-shape depressions in the rock underlying a glacier. They are formed by abrasion when boulders in the glacier are repeatedly caught and released as they are dragged along the bedrock. The rate of glacier erosion varies. Six factors control erosion rate: When

5500-620: The cave floor. These geothermal environments may host geothermal habitats similar to those in Victoria Land and at Deception Island , but Mount Berlin is remote and has never been studied in this regard. It has been evaluated for the potential to obtain geothermal power ; being isolated and extensively covered with ice, these volcanoes are unlikely to have any significant economic value as geothermal resources. Glacier A glacier ( US : / ˈ ɡ l eɪ ʃ ər / ; UK : / ˈ ɡ l æ s i ər , ˈ ɡ l eɪ s i ər / )

5600-575: The coast or nunataks in the ice. Many of these volcanoes form distinct volcanic chains, such as the Executive Committee Range where volcanic activity has shifted westward at a rate of about 1 centimetre per year (0.4 in/year). Such a movement is also apparent in the Flood Range, where activity migrated from Mount Moulton to Mount Berlin. This movement appears to reflect the propagation of crustal fractures, as plate motion

5700-442: The crater, diminishing to 1 metre (3 ft) at Merrem Peak. They were formed by pyroclastic fallout during eruptions, which mantled the topography. As eruption characteristics changed, these processes generated distinct deposits. Tuff deposits containing lapilli and volcanic ash -rich pyroclastic deposits in the crater rim were erupted during hydromagmatic events. Some lava flows feature levee -like forms at their margins. In

5800-571: The created ice's density. The word glacier is a loanword from French and goes back, via Franco-Provençal , to the Vulgar Latin glaciārium , derived from the Late Latin glacia , and ultimately Latin glaciēs , meaning "ice". The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation . The corresponding area of study

5900-467: The deep profile of fjords , which can reach a kilometer in depth as ice is topographically steered into them. The extension of fjords inland increases the rate of ice sheet thinning since they are the principal conduits for draining ice sheets. It also makes the ice sheets more sensitive to changes in climate and the ocean. Although evidence in favor of glacial flow was known by the early 19th century, other theories of glacial motion were advanced, such as

6000-483: The deformation to become a plastic flow rather than elastic. Then, the glacier will begin to deform under its own weight and flow across the landscape. According to the Glen–Nye flow law , the relationship between stress and strain, and thus the rate of internal flow, can be modeled as follows: where: The lowest velocities are near the base of the glacier and along valley sides where friction acts against flow, causing

6100-453: The deposits of magmatic eruption. This is a result of the much higher fragmentation of phreatomagmatic eruptions. Hyaloclastite is glass found with pillow basalts that were produced by non-explosive quenching and fracturing of basaltic glass. These are still classed as phreatomagmatic eruptions, as they produce juvenile clasts from the interaction of water and magma. They can be formed at water depths of >500 m, where hydrostatic pressure

SECTION 60

#1732801051077

6200-400: The deposits of magmatic eruptions, due to the much higher fragmentation of the type of eruption. The deposits appear better sorted than magmatic deposits in the field because of their fine nature, but grain size analysis reveals that the deposits are much more poorly sorted than their magmatic counterparts. A clast known as an accretionary lapilli is distinctive to phreatomagmatic deposits, and

6300-418: The essentially correct explanation in the 1840s, although it was several decades before it was fully accepted. The top 50 m (160 ft) of a glacier are rigid because they are under low pressure . This upper section is known as the fracture zone and moves mostly as a single unit over the plastic-flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in

6400-439: The form of discrete small batches rather than in one large magma chamber . The composition of volcanic rocks varied between eruptions and probably also during different phases of the same eruption. Phonolite was erupted early during volcanic evolution and followed by trachyte during the Quaternary. A long-term trend in iron and sulfur of the tephras may indicate a tendency towards more primitive magma compositions. Mount Berlin

6500-475: The fracture zone. Crevasses form because of differences in glacier velocity. If two rigid sections of a glacier move at different speeds or directions, shear forces cause them to break apart, opening a crevasse. Crevasses are seldom more than 46 m (150 ft) deep but, in some cases, can be at least 300 m (1,000 ft) deep. Beneath this point, the plasticity of the ice prevents the formation of cracks. Intersecting crevasses can create isolated peaks in

6600-403: The glacial base and facilitate sediment production and transport under the same moving speed and amount of ice. Material that becomes incorporated in a glacier is typically carried as far as the zone of ablation before being deposited. Glacial deposits are of two distinct types: Phreatomagmatic Several competing theories exist as to the exact mechanism of ash formation. The most common

6700-453: The glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. However, within high-altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater. Since glacial mass is affected by long-term climatic changes, e.g., precipitation , mean temperature , and cloud cover , glacial mass changes are considered among

6800-428: The glacier will be accommodated by motion in the sediments, or if it'll be able to slide. A soft bed, with high porosity and low pore fluid pressure, allows the glacier to move by sediment sliding: the base of the glacier may even remain frozen to the bed, where the underlying sediment slips underneath it like a tube of toothpaste. A hard bed cannot deform in this way; therefore the only way for hard-based glaciers to move

6900-510: The glacier's surface area, more if the glacier calves icebergs. Ice in the accumulation zone is deep enough to exert a downward force that erodes underlying rock. After a glacier melts, it often leaves behind a bowl- or amphitheater-shaped depression that ranges in size from large basins like the Great Lakes to smaller mountain depressions known as cirques . The accumulation zone can be subdivided based on its melt conditions. The health of

7000-619: The ice at the bottom of the glacier move more slowly than ice at the top. In alpine glaciers, friction is also generated at the valley's sidewalls, which slows the edges relative to the center. Mean glacial speed varies greatly but is typically around 1 m (3 ft) per day. There may be no motion in stagnant areas; for example, in parts of Alaska, trees can establish themselves on surface sediment deposits. In other cases, glaciers can move as fast as 20–30 m (70–100 ft) per day, such as in Greenland's Jakobshavn Isbræ . Glacial speed

7100-420: The ice sheets of Antarctica and Greenland, has been estimated at 170,000 km . Glacial ice is the largest reservoir of fresh water on Earth, holding with ice sheets about 69 percent of the world's freshwater. Many glaciers from temperate , alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause

7200-556: The ice to act as a lever that loosens the rock by lifting it. Thus, sediments of all sizes become part of the glacier's load. If a retreating glacier gains enough debris, it may become a rock glacier , like the Timpanogos Glacier in Utah. Abrasion occurs when the ice and its load of rock fragments slide over bedrock and function as sandpaper, smoothing and polishing the bedrock below. The pulverized rock this process produces

7300-488: The ice, called seracs . Crevasses can form in several different ways. Transverse crevasses are transverse to flow and form where steeper slopes cause a glacier to accelerate. Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally. Marginal crevasses form near the edge of the glacier, caused by the reduction in speed caused by friction of the valley walls. Marginal crevasses are largely transverse to flow. Moving glacier ice can sometimes separate from

7400-411: The idea that meltwater, refreezing inside glaciers, caused the glacier to dilate and extend its length. As it became clear that glaciers behaved to some degree as if the ice were a viscous fluid, it was argued that "regelation", or the melting and refreezing of ice at a temperature lowered by the pressure on the ice inside the glacier, was what allowed the ice to deform and flow. James Forbes came up with

7500-418: The increased pressure can facilitate melting. Most importantly, τ D is increased. These factors will combine to accelerate the glacier. As friction increases with the square of velocity, faster motion will greatly increase frictional heating, with ensuing melting – which causes a positive feedback, increasing ice speed to a faster flow rate still: west Antarctic glaciers are known to reach velocities of up to

7600-423: The infrared OH stretching mode of the water molecule. (Liquid water appears blue for the same reason. The blue of glacier ice is sometimes misattributed to Rayleigh scattering of bubbles in the ice.) A glacier originates at a location called its glacier head and terminates at its glacier foot, snout, or terminus . Glaciers are broken into zones based on surface snowpack and melt conditions. The ablation zone

7700-468: The interaction surface area, leading to explosively rapid cooling rates. The two mechanisms proposed are very similar and the reality is most likely a combination of both. Phreatomagmatic ash is formed by the same mechanisms across a wide range of compositions, basic and acidic. Blocky and equant clasts with low vesicle content are formed. The deposits of phreatomagmatic explosive eruptions are also considered to be better sorted and finer grained than

7800-475: The last 100,000 years Mount Berlin has been more active than Mount Takahe, the other major source of tephra in the West Antarctic, but activity at Berlin was episodic rather than steady. The volcano underwent a surge in activity between 35,000/40,000 and 18,000/20,000 years ago. Despite their size, the eruptions at Mount Berlin did not significantly impact the climate. The eruption history of Mount Berlin

7900-604: The late Pleistocene and the Holocene . Several tephra layers encountered in ice cores all over Antarctica – but in particular at Mount Moulton – have been linked to Mount Berlin, which is the most important source of such tephras in the region. The tephra layers were formed by explosive eruptions that generated high eruption columns . Presently, fumarolic activity occurs at Mount Berlin and forms ice towers from freezing steam. Mount Berlin lies in Marie Byrd Land , West Antarctica , 100 kilometres (62 mi) inland from

8000-493: The magma/water ratio is high, but when there is a lower magma/water ratio the deposits may be coarser and better sorted. There are two types of vent landforms from the explosive interaction of magma and ground or surface water; tuff cones and tuff rings. Both of the landforms are associated with monogenetic volcanoes and polygenetic volcanoes . In the case of polygenetic volcanoes they are often interbedded with lavas, ignimbrites and ash- and lapilli -fall deposits. It

8100-416: The middle Miocene and continued into the later Quaternary ; argon-argon dating yielded ages as young as 8,200 years. Four volcanoes in the Marie Byrd Land Volcanic Province – Mount Berlin, Mount Siple , Mount Takahe and Mount Waesche – were classified as "possibly or potentially active" in the 1990 Antarctic Research Series by LeMasurier et al., and active subglacial volcanoes have been identified on

8200-679: The most deformation. Velocity increases inward toward the center line and upward, as the amount of deformation decreases. The highest flow velocities are found at the surface, representing the sum of the velocities of all the layers below. Because ice can flow faster where it is thicker, the rate of glacier-induced erosion is directly proportional to the thickness of overlying ice. Consequently, pre-glacial low hollows will be deepened and pre-existing topography will be amplified by glacial action, while nunataks , which protrude above ice sheets, barely erode at all – erosion has been estimated as 5 m per 1.2 million years. This explains, for example,

8300-445: The most sensitive indicators of climate change and are a major source of variations in sea level . A large piece of compressed ice, or a glacier, appears blue , as large quantities of water appear blue , because water molecules absorb other colors more efficiently than blue. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing

8400-491: The northern flank, Kraut Rocks at the west-southwestern foot, Walts Cliff on the northeastern flank and Wedemeyer Rocks at the southern foot. The existence of tuyas has been reported from Mount Berlin. According to a 1972 report, tephra overlies ice at some sites. Nonvolcanic features include incipient cirques on the northern and western side. The Marie Byrd Land Volcanic Province features 18 central volcanoes and accompanying parasitic vents , which form islands off

8500-411: The past, certain fallout deposits in the crater rim were thought to be lava flows. Hyalotuff , obsidian and pumice have been recovered from Mount Berlin. Both welded and unwelded pyroclastic and tuffaceous breccias are present. They consist of lava bombs , lithic rocks, obsidian fragments and pumice. Hyaloclastite occurs around the base of Mount Berlin. Most volcanic rocks of Mount Berlin define

8600-725: The pooling of meltwater at the base of the glacier  — perhaps delivered from a supraglacial lake  — or the simple accumulation of mass beyond a critical "tipping point". Temporary rates up to 90 m (300 ft) per day have occurred when increased temperature or overlying pressure caused bottom ice to melt and water to accumulate beneath a glacier. In glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur. These are large scale earthquakes that have seismic magnitudes as high as 6.1. The number of glacial earthquakes in Greenland peaks every year in July, August, and September and increased rapidly in

8700-410: The pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacier ice is slightly more dense than ice formed from frozen water because glacier ice contains fewer trapped air bubbles. Glacial ice has a distinctive blue tint because it absorbs some red light due to an overtone of

8800-580: The range; Wells Saddle separates it from Mount Moulton volcano farther east. Mount Berlin's peak is 2.1 kilometres (1.3 mi) above the highest local elevation of the West Antarctic Ice Sheet . The summit crater (Berlin Crater) is 2 kilometres (1.2 mi) wide and has sharply defined, ice-crowned edges; the highest point of the volcano is on the southeastern margin. Mount Berlin consists of two overlapping edifices: Mount Berlin proper and Merrem Peak 3.5 kilometres (2.2 mi) west-northwest. Merrem Peak

8900-567: The sea, often with an ice tongue , like Mertz Glacier . Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica, Baffin , Devon , and Ellesmere Islands in Canada, Southeast Alaska , and the Northern and Southern Patagonian Ice Fields . As the ice reaches the sea, pieces break off or calve, forming icebergs . Most tidewater glaciers calve above sea level, which often results in

9000-409: The stagnant ice above, forming a bergschrund . Bergschrunds resemble crevasses but are singular features at a glacier's margins. Crevasses make travel over glaciers hazardous, especially when they are hidden by fragile snow bridges . Below the equilibrium line, glacial meltwater is concentrated in stream channels. Meltwater can pool in proglacial lakes on top of a glacier or descend into the depths of

9100-423: The stress being applied, ice will act as an elastic solid. Ice needs to be at least 30 m (98 ft) thick to even start flowing, but once its thickness exceeds about 50 m (160 ft) (160 ft), stress on the layer above will exceeds the inter-layer binding strength, and then it'll move faster than the layer below. This means that small amounts of stress can result in a large amount of strain, causing

9200-438: The surface snowpack may experience seasonal melting. A subpolar glacier includes both temperate and polar ice, depending on the depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is often described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface and is thus frozen to the underlying substrate. A warm-based glacier

9300-595: The top. Phase 2 has ash and lapilli beds that are cross stratified with mega- ripples and dune -like structures. The deposit thicknesses vary from 10 cm to 12 m. Phases 3 and 4 are pyroclastic density current deposits. Phases 1 and 3 were phreatomagmatic. Mount Pinatubo is on the Central Luzon landmass between the South China Sea and the Philippine Sea . The 1991 eruption of Pinatubo

9400-600: The vent. The eruption resumed with phreatomagmatic activity that deposited the Rotongaio Ash. The Grímsvötn volcano in Iceland is a sub-glacial volcano, located beneath the Vatnajökull ice cap. For a typical sub-glacial eruption, overlying glacial ice is melted by the heat of the volcano below, and the subsequent introduction of meltwater to the volcanic system results in a phreatomagmatic explosion. Grímsvötn

9500-546: The volcano is 3,478 metres (11,411 ft) above sea level. It has a volume of 200 cubic kilometres (48 cu mi) and rises from the West Antarctic Ice Sheet . It is part of the Marie Byrd Land Volcanic Province . Trachyte is the dominant volcanic rock and occurs in the form of lava flows and pyroclastic rocks . The volcano began erupting during the Pliocene and was active into

9600-417: The weight of the ice is supported by the underlying water, and the glacier is afloat. Glaciers may also move by basal sliding , where the base of the glacier is lubricated by the presence of liquid water, reducing basal shear stress and allowing the glacier to slide over the terrain on which it sits. Meltwater may be produced by pressure-induced melting, friction or geothermal heat . The more variable

9700-500: The western and northern rim of Berlin Crater. Their existence was first reported in 1968; ice towers form when fumarole exhalations freeze in the cold Antarctic atmosphere and are a characteristic trait of Antarctic volcanoes. ASTER satellite imaging has not detected these fumaroles, presumably because they are hidden within the ice towers. A more than 70-metre-long (230 ft) ice cave begins at one of these ice towers; temperatures of over 12 °C (54 °F) have been recorded on

9800-448: Was andesite and dacite in the pre-climactic phase but only dacite in the climactic phase. The climactic phase had a volume of 3.7–5.3 km . The eruption consisted of sequentially increasing ash emissions, dome growth, 4 vertical eruptions with continued dome growth, 13 pyroclastic flows and a climactic vertical eruption with associated pyroclastic flows. The pre-climactic phase was phreatomagmatic. The Hatepe eruption in 232 ± 12 AD

9900-487: Was active from the Pliocene into the Holocene . The oldest parts are found at Wedemeyer Rocks and Brandenberger Bluff and are 2.7 million years old. Activity then took place at Merrem Peak between 571,000 and 141,000 years ago; during this phase eruptions also occurred on the flanks of Mount Berlin. After 25,500 years ago activity shifted to Mount Berlin proper and the volcano grew by more than 400 metres (1,300 ft). Over time, volcanic activity on Mount Berlin has moved in

10000-592: Was the latest major eruption at Lake Taupō in New Zealand 's Taupō Volcanic Zone . There was minor initial phreatomagmatic activity followed by the dry venting of 6 km of rhyolite forming the Hatepe Plinian Pumice. The vent was then infiltrated by large amounts of water causing the phreatomagmatic eruption that deposited the 2.5 km Hatepe Ash. The water eventually stopped the eruption though large amounts of water were still erupted from

#76923