Misplaced Pages

#952047

55-621: Jorge Montt Glacier is a tidewater glacier located in the Aisén Region of Chile , south of the town of Caleta Tortel . It lies at the north end of the Southern Patagonian Ice Field , within Bernardo O'Higgins National Park . The mouth of Pascua River is located in the vicinity of the glacier calving front. The total drainage area of the glacier is about 510 km (200 sq mi). The glacier's ice

110-449: A first-order control on the advance/retreat cycle of calving glaciers during most of the advance retreat cycle, but there are climate insensitive periods as well. Pelto (1987) examined the terminus behavior of 90 Alaskan glaciers and found that the terminus behavior of all 90 were correctly predicted based on the AAR and calving rate. If we begin at the stable retracted position at the end of

165-409: A glacier or ice sheet. It may consist of partly rounded particles ranging in size from boulders (in which case it is often referred to as boulder clay) down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called glacial flour . Lateral moraines are those formed at the side of the ice flow, and terminal moraines are those formed at the foot, marking the maximum advance of

220-466: A glacier, AAR, is the percentage of a glacier that is a snow-covered accumulation zone at the end of the summer melt season. This percentage for large Alaskan glaciers is between 60 and 70 for non-calving glaciers, 70-80 for moderately calving glaciers and up to 90 for very high calving rate glaciers. By using accumulation area ratio (AAR) data for Alaskan tidewater calving glaciers, Pelto (1987) and Viens (1995) produced models showing that climate acts as

275-417: A long moraine bank marking the ice margin. Several processes may combine to form and rework a single moraine, and most moraines record a continuum of processes. Reworking of moraines may lead to the formation of placer deposits of gold as is the case of southernmost Chile . Moraines can be classified either by origin, location with respect to a glacier or former glacier, or by shape. The first approach

330-424: A major retreat of 8.5 km in those 25 years as a result of rapid thinning [1] . At some point the glacier reaches a pinning point where calving is reduced due to a fjord narrowing or shoaling and the glacier's AAR is near 100. This is occurring with LeConte Glacier and Yahtse Glacier . Le Conte Glacier currently has an AAR of 90, is at a retracted position and seems likely to be set to advance after building

385-701: A mile in the course of the year." Rivera's study showed the glacier's unique rate of retreat was primarily a function of the fjord's peculiar bathymetry; secondarily a result of a warming climate. In 2010 remnants of nothofagus (southern beech) were discovered and later dated, "yielding burial ages between 460 and 250 cal yrs BP." According to Rivera: "The tree-ring results suggest the area was covered by an old-growth forest dominated by Nothofagus betuloides ("coigue de Magallanes" – Magellanic southern beech) with individuals of average age close to 150 years, co-existing for almost 300 years (total chronology length). The radiocarbon ages of between 250 and 450 years BP from two of

440-499: A reduced rate of 37 m⋅a . In 1990, the Taku Glacier's AAR was 82 high enough, to prompt Pelto and Miller to conclude that the Taku Glacier would continue to advance for the remaining decade of the 20th century. From 1986 to 2005, the equilibrium line altitude on the glacier rose without a significant terminus shift causing the AAR to decline to about 72. Pelto and Miller concluded that the current reduction in rate of advance

495-471: A relationship between calving speed and water depth based on analysis of six glaciers that calve into lakes. They found that the same basic calving relationship developed for tidewater calving glaciers was true for freshwater calving glaciers, only the calving coefficients led to calving rates 10% of that for tidewater glaciers. Observations of Alaskan tidewater calving glaciers prompted Austin Post to describe

550-428: A terminal moraine. They form perpendicular to the lateral moraines that they reside between and are composed of unconsolidated debris deposited by the glacier. They are created during temporary halts in a glacier's retreat. In permafrost areas an advancing glacier may push up thick layers of frozen sediments at its front. An arctic push moraine will then be formed. A medial moraine is a ridge of moraine that runs down

605-460: A terminus shoal. The drop in calving rate allows the glacier to reestablish equilibrium. The Taku Glacier provides a good example of this cycle. It was at its maximum extent near 1750. At this point it had closed off Taku Inlet . Subsequently, calving retreat commenced. By the time John Muir saw the glacier in 1890, it was near its minimum extent, at a location where the fjord narrowed, with deep water in front. About 1900, its AAR of 90 led to

SECTION 10

#1732791275953

660-408: A tidewater glacier cycle the glacier will have a moderate calving rate and a high AAR, above 70. The glacier will build a terminus shoal of sediment further reducing the calving rate. This will improve the glacier mass balance and the glacier can begin to advance due to this change or an increase in ice flux to the terminus due to increasing snowfall or reduced snow melt. As the advance proceeds

715-409: Is also a function of resulting changes in fjord geometry, and calving rate at the glacier terminus as it changes position. Calving glaciers are different from land terminating glaciers in the variation in velocity along their length. Land terminating glacier velocities decline as the terminus is approached. Calving glaciers accelerate at the terminus. A declining velocity near the terminus slows

770-550: Is not sensitive to climate during the advancing and drastically retreating phases of its cycle. In the same region, disparate terminus responses are observed amongst tidewater calving glaciers, but not land terminating glaciers. This is exemplified by the 17 major glaciers of the Juneau Icefield , 5 have retreated more than 500 m since 1948, 11 more than 1000 m, and one glacier the Taku has advanced. This difference highlights

825-440: Is since 1970 is attributable to the laterally expanding terminal lobe as opposed to declining mass balance and that the primary force behind the Taku Glacier's advance since about 1900 is due to positive mass balance. The recent lack of positive mass balance will eventually slow the retreat if it persists. The size of tidewater glaciers is such that the tidewater glacier cycle is several hundred years in length. A tidewater glacier

880-450: Is suitable for moraines associated with contemporary glaciers—but more difficult to apply to old moraines , which are defined by their particular morphology, since their origin is debated. Some moraine types are known only from ancient glaciers, while medial moraines of valley glaciers are poorly preserved and difficult to distinguish after the retreat or melting of the glacier. Lateral moraines are parallel ridges of debris deposited along

935-421: Is the key variable in predicting calving of a tidewater glacier. Debris flux and sediment recycling at the glacier grounding-line, particularly rapid in the temperate glaciers of Alaska, can alter this depth, acting as a second-order control on terminus fluctuations. This effect contributes to the insensitivity of a glacier to climate when its terminus is either retreating or advancing in deep water. Austin Post

990-465: Is the large retreat of Glacier Bay and Icy Bay glaciers in Alaska that occurred rapidly via this process. Muir Glacier retreated 33  km from 1886 to 1968 featuring extensive calving the entire time. It reversed its retreat briefly 1890—1892. In 1968, Muir Glacier was still 27 km long, less than half of its length in 1886. The retreat continued an additional 6.5 km by 2001. Today,

1045-467: Is the mean water depth at glacier front (m) and D {\displaystyle D} is a constant (0 m⋅a ). Pelto and Warren (1991) found a similar calving relationship with tidewater glaciers observed over longer time periods, with slightly reduced calving rate to the mainly summer rates noted by Brown et al. (1982). Calving is an important form of ablation for glaciers that terminate in freshwater , also. Funk and Röthlisberger determined

1100-414: Is thinning most at low elevations, where air temperature is the highest. Ice thinning between 1975 and 2000 averaged 3.3 m (11 ft) per year over the entire glacier, and reached 18 m (59 ft) per year at the lowest elevations. The glacier calving front experienced a major retreat of 8.5 km (5.3 mi) in those 25 years as a result of rapid thinning. The glacier calves off icebergs into

1155-540: The Baker Channel . In 2000, NASA wrote: Conventional topographic data from the 1970s and 1990s were compared with data from NASA's February 2000 Shuttle Radar Topography Mission to measure changes in the volumes of the 63 largest glaciers in the region over time. The researchers concluded the thinning rate of the Patagonia Icefields more than doubled during the period from 1995 through 2000 versus

SECTION 20

#1732791275953

1210-475: The Taku Glacier onset of advance, at the same time that the remaining Juneau Icefield glaciers continued receding. This advance continued at a rate of 88 m⋅a , advancing 5.3 km from the 1900 minimum until 1948, all the while building and then riding up on a substantial outwash plain beneath its calving face. After 1948, the now non-calving Taku Glacier, possessed an AAR only slightly reduced (86 and 63). This drove 1.5 km of further advance at

1265-491: The beginning of the 20th century, the coastline was nearly straight and the bay non-existent. The entrance of the bay was filled by a tidewater glacier face that calved icebergs directly into the Gulf of Alaska. A century later glacier retreat has opened a multi-armed bay more than 30 miles long. The tidewater glacier has divided into three independent glaciers, Yahtse, Tsaa and Guyot Glacier. Other examples of glaciers currently in

1320-402: The calving process; this increases the export of icebergs from the glacier. Large calving retreats are initiated by warming conditions causing ice thinning. The resulting retreat to a new equilibrium conditions can be far more extensive than will be regained during the next advance stage. A good example of this is Muir Glacier. Next to Glacier Bay, Icy Bay has had the most extensive retreat. At

1375-563: The case of Brady Glacier. Usually substantial thinning occurs before retreat from the shoal commences. This allowed the prediction in 1980, by the United States Geological Survey (USGS), of the retreat of the Columbia Glacier from its terminus shoal. The glacier had remained on this shoal throughout the entire 20th century. The USGS was monitoring the glacier due to its proximity to Valdez, Alaska ,

1430-603: The center of a valley floor. It forms when two glaciers meet and the debris on the edges of the adjacent valley sides join and are carried on top of the enlarged glacier. As the glacier melts or retreats, the debris is deposited and a ridge down the middle of the valley floor is created. The Kaskawulsh Glacier in the Kluane National Park , Yukon , has a ridge of medial moraine 1 km wide. Supraglacial moraines are created by debris accumulated on top of glacial ice. This debris can accumulate due to ice flow toward

1485-416: The cycle. Taku Glacier which has been advancing for 120 years no longer calves. Hubbard Glacier still has a calving front. The glacier will then expand until the AAR is between 60 and 70 and equilibrium of the non-calving glacier is achieved. The glacier is not very sensitive to climate during the advance as its AAR is quite high, when the terminus shoal is limiting calving. At the maximum extended position

1540-427: The following relationship between calving speed and water depth: V C = C H w + D {\displaystyle V_{C}=CH_{w}+D} , where V C {\displaystyle V_{C}} is the mean calving speed ( m ⋅ a ), C {\displaystyle C} is a calving coefficient (27.1±2 a ), H w {\displaystyle H_{w}}

1595-479: The glacier fracturing and separating, or calving , from the ice front as icebergs. Climate change causes a shift in the equilibrium line altitude (ELA) of a glacier. This is the imaginary line on a glacier, above which snow accumulates faster than it ablates, and below which, the reverse is the case. This altitude shift, in turn, prompts a retreat or advance of the terminus toward a new steady-state position. However, this change in terminus behavior for calving glaciers

1650-511: The glacier has melted. Moraines may form through a number of processes, depending on the characteristics of sediment, the dynamics on the ice, and the location on the glacier in which the moraine is formed. Moraine forming processes may be loosely divided into passive and active . Passive processes involve the placing of chaotic supraglacial sediments onto the landscape with limited reworking, typically forming hummocky moraines. These moraines are composed of supraglacial sediments from

1705-415: The glacier is near the head of its fjord and with minimal calving the glacier may be stable at this retracted position. The best current example is illustrated by the United States Geological Survey study of Columbia Glacier. They noted that the average calving rate from Columbia Glacier increased from 3 km ⋅a in the second half of 1983 to 4 km ⋅a during the first nine months of 1984. This rate

Jorge Montt Glacier - Misplaced Pages Continue

1760-419: The glacier is once again sensitive to changing climate. Brady Glacier and Baird Glacier are examples of glaciers currently at this point. Brady Glacier has been thinning during the last two decades due to the higher equilibrium line altitudes accompanying warmer conditions in the region, and its secondary termini have begun to retreat. A glacier can remain at this position for sometime, a century at least in

1815-428: The glacier margin (up to 80 degrees) than further away (where slopes are typically 29 to 36 degrees. Ground moraines are till-covered areas with irregular topography and no ridges, often forming gently rolling hills or plains, with relief of less than 10 meters (33 ft). Ground moraine is accumulated at the base of the ice as lodgment till with a thin and discontinuous upper layer of supraglacial till deposited as

1870-465: The glacier response to climate. An accelerating velocity at the front enhances the speed of the glaciers response to climate or glacier dynamic changes. This is observed in Svalbard , Patagonia and Alaska . A calving glacier requires more accumulation area than a land terminating glacier to offset this higher loss from calving. The calving rate is largely controlled by the depth of the water and

1925-416: The glacier retreats from the shoal, causing ever more rapid glacier flow, calving and retreat. A glacier is comparatively insensitive to climate during this calving retreat. However, in the case of San Rafael Glacier , Chile , a switch from retreat (1945–1990) to advance (1990–1997) was noted. Current examples of this retreat are Columbia Glacier and Guyot Glacier . The most famous recent example of this

1980-544: The glacier retreats. It typically is found in the areas between end moraines. Rogen moraines or ribbed moraines are a type of basal moraines that form a series of ribs perpendicular to the ice flow in an ice sheet . The depressions between the ribs are sometimes filled with water, making the Rogen moraines look like tigerstripes on aerial photographs . Rogen moraines are named after Lake Rogen in Härjedalen , Sweden ,

2035-417: The glacier velocity at the calving front. The process of calving provides an imbalance in forces at the front of the glaciers, that raises velocity. The depth of the water at the glacier front is a simple measure that allows estimation of calving rate, but is the amount of flotation of the glacier at the front that is the specific physical characteristic that is important. Water depth at the glacier terminus

2090-408: The glacier would retreat 32 km before stabilizing. By 2006, it has retreated 16 km. The water remains deep and the calving rate and glacier velocity very high, indicating retreat will continue. At this point, just like having a balloon payment in an adjustable rate mortgage, the glacier has to pay a whole new portion of its balance via icebergs. The glacier accelerates as flow is enhanced by

2145-578: The glacier. Other types of moraine include ground moraines ( till -covered areas forming sheets on flat or irregular topography ) and medial moraines (moraines formed where two glaciers meet). The word moraine is borrowed from French moraine [mɔ.ʁɛn] , which in turn is derived from the Savoyard Italian morena ('mound of earth'). Morena in this case was derived from Provençal morre ('snout'), itself from Vulgar Latin * murrum ('rounded object'). The term

2200-415: The ice surface. Active processes form or rework moraine sediment directly by the movement of ice, known as glaciotectonism. These form push moraines and thrust-block moraines, which are often composed of till and reworked proglacial sediment. Moraine may also form by the accumulation of sand and gravel deposits from glacial streams emanating from the ice margin. These fan deposits may coalesce to form

2255-503: The landform's type locality. Closely related to Rogen moraines, de Geer moraines are till ridges up to 5m high and 10–50m wide running perpendicular to the ice flow. They occur in large groups in low-lying areas. Named for Gerard De Geer , who first described them in 1889, these moraines may have developed from crevasses underneath the ice sheet. The Kvarken has a very high density of de Geer moraines. End moraines, or terminal moraines , are ridges of unconsolidated debris deposited at

Jorge Montt Glacier - Misplaced Pages Continue

2310-411: The moraine. There are two types of end moraines: terminal and recessional. Terminal moraines mark the maximum advance of the glacier. Recessional moraines are small ridges left as a glacier pauses during its retreat. After a glacier retreats, the end moraine may be destroyed by postglacial erosion. Recessional moraines are often observed as a series of transverse ridges running across a valley behind

2365-401: The period from 1975 to 2000. In December 2011, a new study was published. "The study was presented by glaciologist and CECs researcher Andrés Rivera, who focused his investigation on changes in the glacier between February 2010 and January 2011. Using a series of 1,445 photos taken throughout this period, scientists found that the glacier shrank roughly 82 feet each day, receding more than half

2420-528: The port for crude oil export from the Alaskan Pipeline . At some point a decline in mass balance will trigger a retreat from the shoal into deeper water at which point calving will ensue. Based on the recent thinning it is suggested that Brady Glacier is poised to begin retreat. The calving rate will increase as the glacier retreats from the shoal into the deeper fjord just cleared by the glacier during advance. The water depth initially increases as

2475-554: The retreat phase are South Sawyer and Sawyer Glaciers in Alaska, retreating 2.1 and 2.3 km respectively from 1961 to 2005. In Patagonia an example of a rapidly retreating glacier is the Jorge Montt Glacier which drains into Baja Jorge Montt in the Pacific Ocean. The glacier's ice thinning, at low elevations, from 1975 to 2000 reached 18 m⋅a at the lowest elevations. The glacier calving front experienced

2530-473: The sampled trees suggest that the tree ring samples were taken from a mature forest that was destroyed by the advance of Glaciar Jorge Montt during the LIA period." Tidewater glacier While climate is the main factor affecting the behavior of all glaciers, additional factors affect calving ( iceberg -producing) tidewater glaciers. These glaciers terminate abruptly at the ocean interface, with large pieces of

2585-454: The sides of a glacier. The unconsolidated debris can be deposited on top of the glacier by frost shattering of the valley walls or from tributary streams flowing into the valley, or may be subglacial debris carried to the surface of the glacier, melted out, and transported to the glacier margin. Lateral moraines can rise up to 140 meters (460 ft) over the valley floor, can be up to 3 kilometers (1.9 mi) long, and are steeper close to

2640-427: The snout or end of the glacier. They usually reflect the shape of the glacier's terminus . Glaciers act much like a conveyor belt, carrying debris from the top of the glacier to the bottom where it deposits it in end moraines. End moraine size and shape are determined by whether the glacier is advancing, receding or at equilibrium. The longer the terminus of the glacier stays in one place, the more debris accumulate in

2695-419: The surface in the ablation zone , melting of surface ice or from debris that falls onto the glacier from valley sidewalls. Washboard moraines , also known as minor or corrugated moraines , are low-amplitude geomorphic features caused by glaciers. They consist of low-relief ridges, 1 to 2 meters (3 ft 3 in to 6 ft 7 in) in height and around 100 meters (330 ft) apart, accumulated at

2750-495: The terminus shoal will be pushed in front of the glacier and continue to build, keeping the calving rate low. In the case of the most glaciers such as the Taku Glacier the glacier will eventually build a terminus shoal that is above water and calving will essentially cease. This will eliminate this loss of ice from the glacier and the glacier can continue to advance. Taku Glacier and Hubbard Glacier have been in this phase of

2805-430: The tidewater calving glacier advance/retreat cycle: (1) advancing, (2) stable-extended, (3) drastically retreating, or (4) stable-retracted. The following is a detailed review of the tidewater glacier cycle derived by Post, with numerous cited examples, the cycle is based on observations of temperate tidewater glaciers in Alaska, not outlet glaciers from large ice sheets or polar glaciers. The accumulation area ratio of

SECTION 50

#1732791275953

2860-609: The unique impacts on terminus behavior of the tidewater glacier cycle, which has caused the Taku Glacier to be insensitive to climate change in the last 60 years. Concurrently, in both Patagonia and Alaska, there are tidewater glaciers that have advanced for a considerable period, tidewater glaciers undergoing rapid retreat and stable tidewater glaciers. Moraine A moraine is any accumulation of unconsolidated debris ( regolith and rock ), sometimes referred to as glacial till , that occurs in both currently and formerly glaciated regions, and that has been previously carried along by

2915-451: Was four times greater than that measured at the end of 1977 and increased again in 1985. The glacier flow, i.e., the movement of the ice toward the sea, also increased, it was inadequate to keep pace with the break-up and expulsion of icebergs. The increase in speed instead seemed to just feed the ever faster conveyor to the terminus for iceberg production. This prompted the USGS to predict that

2970-467: Was introduced into geology by Horace Bénédict de Saussure in 1779. Moraines are landforms composed of glacial till deposited primarily by glacial ice. Glacial till, in turn, is unstratified and unsorted debris ranging in size from silt -sized glacial flour to large boulders. The individual rock fragments are typically sub-angular to rounded in shape. Moraines may be found on the glacier's surface or deposited as piles or sheets of debris where

3025-437: Was one of the first to propose that water depth at the calving margin strongly affects the rate of iceberg calving. Glaciers that terminate on a morainal shoal are generally stable, but once a glacier retreats into water that deepens as the ice front recedes, calving rate increases rapidly and results in drastic retreat of the terminus. Using data collected from 13 Alaskan tidewater calving glaciers, Brown et al. (1982) derived

#952047