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41-583: Pitt Lake is in a typical U-shaped glacial valley in the Pacific Ranges of the Coast Mountains . The overdeepening of the lower end of the valley over the span of the Wisconsin glaciation created a trough over 140 m below current sea level. After initial glacial retreat at around 13,000 years ago a saltwater fjord occupied this basin when relative sea levels were still ca 120 to 140m above current levels in

82-407: A U-shaped, glaciated valley is often stepwise where flat basins are interrupted by thresholds. Rivers often dig a V-shaped valley or gorge through the threshold. Surrounding smaller tributary valleys will often join the main valleys during glaciation periods, leaving behind features known as hanging valleys high in the trough walls after the ice melts. After deglaciation, snow and ice melt from

123-415: A characteristic U shape in cross-section, with steep, straight sides and a flat or rounded bottom (by contrast, valleys carved by rivers tend to be V-shaped in cross-section). Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within

164-688: A classic U-shaped valley that is also a fjord is the Western Brook Pond Fjord in Gros Morne National Park in Newfoundland , Canada. Formation of a U-shaped valley happens over geologic time , meaning not during a human's lifespan. It can take anywhere between 10,000 and 100,000 years for a V-shaped valley to be carved into a U-shaped valley. These valleys can be several thousand feet deep and tens of miles long. Glaciers will spread out evenly in open areas, but tend to carve deep into

205-515: A cover of till. Interpreting the glacial history of landforms can be difficult due to the tendency of overprinting landforms on top of each other. As a glacier melts, large amounts of till are eroded and become a source of sediments for reworked glacial drift deposits. These include glaciofluvial deposits , such as outwash in sandurs , and as glaciolacustrine and glaciomarine deposits, such as varves (annual layers) in any proglacial lakes which may form. Erosion of till may take place even in

246-453: A gold deposit would be found in the region of Pitt Lake. Historian Garnet Basque states that geologists are convinced that the region around Pitt Lake is not gold bearing. The lost mine of Pitt Lake is a story without scientific support. Glacial valley U-shaped valleys , also called trough valleys or glacial troughs , are formed by the process of glaciation . They are characteristic of mountain glaciation in particular. They have

287-466: A higher water content behave more fluidly, and thus are more susceptible to flow. There are three main types of flows, which are listed below. In cases where till has been indurated or lithified by subsequent burial into solid rock, it is known as the sedimentary rock tillite . Matching beds of ancient tillites on opposite sides of the south Atlantic Ocean provided early evidence for continental drift . The same tillites also provide some support to

328-473: A locality named Alvin , which is a transport and shipping point for logging companies and their employees. Pitt Lake has an oceanic climate ( Köppen climate type Cfb ). As such, it features cool, rainy winters with relatively warm and dry summers. The average annual precipitation is 2,155.4 mm (84.86 in). Extremes vary from −23.3 °C (−9.9 °F), recorded on January 23, 1969, to 37.0 °C (98.6 °F), recorded on July 21, 2006. The lake

369-510: Is a form of glacial drift , which is rock material transported by a glacier and deposited directly from the ice or from running water emerging from the ice. It is distinguished from other forms of drift in that it is deposited directly by glaciers without being reworked by meltwater. Till is characteristically unsorted and unstratified , and is not usually consolidated . Most till consists predominantly of clay, silt , and sand , but with pebbles, cobbles, and boulders scattered through

410-417: Is likely eroded from bedrock rather than being created by glacial processes. The sediments carried by a glacier will eventually be deposited some distance down-ice from its source. This takes place in the ablation zone , which is the part of the glacier where the rate of ablation (removal of ice by evaporation, melting, or other processes) exceeds the rate of accumulation of new ice from snowfall. As ice

451-455: Is popular with boaters and canoeists, but is prone to heavy winds and rains as well as big waves (due to its great depth). The Upper Pitt, meaning the valley upstream from the lake, is considered one of BC's best fly-fishing rivers and one of its best steelhead streams. In addition, there is a destination golfing resort in the Pitt Polder area called Swan-e-set. The area along the east side of

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492-456: Is quite soft and it was unbelievable to many that it could be responsible for the severe carving of bedrock characteristic of glacial erosion. German geologist Penck and American geologist Davis were vocal supporters of this unprecedented glacial erosion. Progress was made in the 1970s and 1980s on the possible mechanisms of glacial erosion and U-shaped valleys via models proposed by various scientists. Numerical models have been created to explain

533-705: Is removed, debris are left behind as till. The deposition of glacial till is not uniform, and a single till plain can contain a wide variety of different types of tills due to the various erosional mechanisms and location of till with respect to the transporting glacier. The different types of till can be categorized between subglacial (beneath) and supraglacial (surface) deposits. Subglacial deposits include lodgement, subglacial meltout, and deformation tills. Supraglacial deposits include supraglacial meltout and flow till. Supraglacial deposits and landforms are widespread in areas of glacial downwasting (vertical thinning of glaciers, as opposed to ice-retreat. They typically sit at

574-724: The Lake District , Yosemite Valley , and the Rottal and Engstlige  [ de ] valleys in Switzerland . Glacial troughs also exist as submarine valleys on continental shelves, such as the Laurentian Channel . These geomorphic features significantly influence sediment distribution and biological communities through their modification of current patterns. Geologists did not always believe that glaciers were responsible for U-shaped valleys and other glacial erosional features. Ice

615-548: The Precambrian Snowball Earth glaciation event hypothesis. Tills sometimes contain placer deposits of valuable minerals such as gold. Diamonds have been found in glacial till in the north-central United States and in Canada. Till prospecting is a method of prospecting in which tills are sampled over a wide area to determine if they contain valuable minerals, such as gold, uranium, silver, nickel, or diamonds, and

656-555: The Principal Cordillera of the Andes, glacial valley floors may be covered by thick lava flows . A glacial trough or glaciated mountain valley often ends in an abrupt head known as the 'trough end' or 'trough head'. This may have almost sheer rock walls and spectacular waterfalls . They are believed to have been formed where a number of small glaciers merge to produce a much larger glacier. Examples include: Warnscale Bottom in

697-840: The Scottish Highlands . A classic glacial trough is in Glacier National Park in Montana , USA in which the St. Mary River runs. Another well-known U-shaped valley is the Nant Ffrancon valley in Snowdonia , Wales . When a U-shaped valley extends into saltwater, becoming an inlet of the sea, it is called a fjord , from the Norwegian word for these features that are common in Norway. Outside of Norway,

738-434: The entrainment by the moving ice of previously available unconsolidated sediments. Bedrock can be eroded through the action of glacial plucking and abrasion , and the resulting clasts of various sizes will be incorporated to the glacier's bed. Glacial abrasion is the weathering of bedrock below a flowing glacier by fragmented rock on the basal layer of the glacier. The two mechanisms of glacial abrasion are striation of

779-450: The bedrock by coarse grains moved by the glacier, thus gouging the rock below, and polishing of the bedrock by smaller grains such as silts. Glacial plucking is the removal of large blocks from the bed of a glacier. Much of the silt in till is produced by glacial grinding, and the longer the till remains at the ice-bedrock interface, the more thoroughly it is crushed. However, the crushing process appears to stop with fine silt. Clay in till

820-498: The clasts dipping upstream. Though till is generally unstratified, till high in clay may show lamination due to compaction under the weight of overlying ice. Till may also contain lenses of sand or gravel , indicating minor and local reworking by water transitional to non-till glacial drift. The term till comes from an old Scottish name for coarse, rocky soil. It was first used to describe primary glacial deposits by Archibald Geikie in 1863. Early researchers tended to prefer

861-634: The contact surfaces with greatest resistance to flow, and the resulting section minimises friction. There are two main variations of this U-shape. The first is called the Rocky Mountain model and it is attributed to alpine glacial valleys, showing an overall deepening effect on the valley. The second variation is referred to as the Patagonia-Antarctica model, attributed to continental ice sheets and displaying an overall widening effect on its surroundings. The floors of these glacial valleys are where

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902-413: The difficulties in accurately classifying different tills, which are often based on inferences of the physical setting of the till rather than detailed analysis of the till fabric or particle size. Subglacial lodgement tills are deposits beneath the glacier that are forced, or "lodged" into the bed below. As glaciers advance or retreat, the clasts that are deposited by the ice may have a lower velocity than

943-644: The east. The other fjord-lakes include Coquitlam Lake , Alouette Lake , Stave Lake , and Chehalis Lake . The Pitt River drains into the northern end of Pitt Lake. The western shore of Pitt Lake are protected within Pinecone Burke Provincial Park , while most of the eastern shore are protected within Golden Ears Provincial Park . The southern end of Pitt Lake features an extensive marshland called Pitt Polder . While most of this marshland has since been drained for agricultural use,

984-410: The glacier. Many of the clasts are faceted, striated, or polished, all signs of glacial abrasion . The sand and silt grains are typically angular to subangular rather than rounded. It has been known since the careful statistic work by geologist Chauncey D. Holmes in 1941 that elongated clasts in tills tend to align with the direction of ice flow. Clasts in till may also show slight imbrication , with

1025-411: The glacier. Since the rate of deposition is controlled by the rate of basal melting, it is worth considering the factors that contribute to melting. These can be the geothermal heat flux, frictional heat generated by sliding, ice thickness, and ice-surface temperature gradients. Subglacial deformation tills refer to the homogenization of glacial sediments that occur when the stresses and shear forces from

1066-401: The glacier. These consist of clasts and debris that become exposed due to melting via solar radiation. These debris are either just debris that have a high relative position on the glacier, or clasts that have been transported up from the base of the glacier. Debris accumulation has a feedback-loop relationship with melting. Initially, the darker colored debris absorb more heat and thus accelerate

1107-403: The ground when confined to a valley. Ice thickness is a major contributing factor to valley depth and carving rates. As a glacier moves downhill through a valley, usually with a stream running through it, the shape of the valley is transformed. As the ice melts and retreats, the valley is left with very steep sides and a wide, flat floor. This parabolic shape is caused by glacial erosion removing

1148-403: The ice itself. When the friction between the clast and the bed exceeds the forces of the ice flowing above and around it, the clast will cease to move, and it will become a lodgement till. Subglacial meltout tills are tills that are deposited via the melting of the ice lobe. Clasts are transported to the base of the glacier over time, and as basal melting continues, they are slowly deposited below

1189-748: The ice, called glacial till or glacial erratic . Examples of U-shaped valleys are found in mountainous regions throughout the world including the Andes , Alps , Caucasus Mountains , Himalaya , Rocky Mountains , New Zealand and the Scandinavian Mountains . They are found also in other major European mountains including the Carpathian Mountains , the Pyrenees , the Rila and Pirin mountains in Bulgaria , and

1230-453: The lake is somewhat notorious for being the reputed location of Slumach 's lost gold mine , the location of many failed and sometimes disastrous searches for the alleged murderer's lost gold mine. Local historian Bill Barlee has said "that this highly colourful and interesting tale, accepted as fact by a host of treasure seekers, probably does not exist." According to Barlee by the geological information available it would appear unlikely that

1271-650: The melting process. After a significant amount of melting has occurred, the thickness of the till insulates the ice sheet and slows the melting process. Supraglacial meltout tills typically end up forming moraines. Supraglacial flow tills refer to tills that are subject to a dense concentration of clasts and debris from meltout. These debris localities are then subsequently affected by ablation . Due to their unstable nature, they are subject to downslope flow, and thus named "flow till." Properties of flow tills vary, and can depend on factors such as water content, surface gradient, and debris characteristics. Generally, flow tills with

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1312-799: The most evidence can be found regarding glaciation cycles. For the most part, the valley floor is wide and flat, but there are various glacial features that signify periods of ice transgression and regression. The valley can have various steps, known as valley steps , and over-deepenings anywhere from ten to hundreds of meters deep. These then fill in with sediments to create plains or water to create lakes, sometimes referred to as "string-of-pearl" or ribbon lakes. Such water filled U-valley basins are also known as "fjord-lakes" or "valley-lakes" (Norwegian: fjordsjø or dalsjø ). Gjende and Bandak lakes in Norway are examples of fjord -lakes. Some of these fjord-lakes are very deep for instance Mjøsa (453 meters) and Hornindalsvatnet (514 m). The longitudinal profile of

1353-488: The mountain tops can create streams and rivers in U-shaped valleys. These are referred to as misfit streams. The streams that form in hanging valleys create waterfalls that flow into the main valley branch. Glacial valleys may also have natural, often dam-like, structures within them, called moraines . They are created due to excess sediment and glacial till moved and deposited by the glacier. In volcanic mountain ranges, such as

1394-470: The moving glacier rework the topography of the bed. These contain preglacial sediments (non glacial or earlier glacial sediments), which have been run over and thus deformed by meltout processes or lodgement. The constant reworking of these deposited tills leads to a highly homogenized till. Supraglacial meltout tills are similar to subglacial meltout tills. Rather than being the product of basal melting, however, supraglacial meltout tills are imposed on top of

1435-516: The northernmost portion is strictly protected in order to provide critical habitat for migratory birds. The community of Pitt Meadows and the Katzie First Nations reserve of Pitt Lake Indian Reserve 4 are located at the southern end of the lake. Just southwest of the lake is the community of Port Coquitlam , which is across the Pitt River from Pitt Meadows . At the north end of the lake is

1476-486: The phenomenon of carving U-shaped valleys. Till Till or glacial till is unsorted glacial sediment . Till is derived from the erosion and entrainment of material by the moving ice of a glacier . It is deposited some distance down-ice to form terminal , lateral , medial and ground moraines . Till is classified into primary deposits, laid down directly by glaciers, and secondary deposits, reworked by fluvial transport and other processes. Till

1517-508: The region. Unlike neighbouring Indian Arm and Howe Sound farther west, this fjord basin became partly cut off from tidal waters by sedimentation of the lower Fraser River ca 10,500 years ago, and Pitt Lake is now considered a tidal fjord lake. Pitt Lake is the second largest of a series of north–south oriented fjord-lakes incising the southern slopes of the Pacific Ranges, the largest being Harrison Lake located 60 km (37 mi) to

1558-464: The subglacial environment, such as in tunnel valleys . There are various types of classifying tills: Traditionally (e.g. Dreimanis , 1988 ) a further set of divisions has been made to primary deposits, based upon the method of deposition. Van der Meer et al. 2003 have suggested that these till classifications are outdated and should instead be replaced with only one classification, that of deformation till. The reasons behind this are largely down to

1599-412: The term boulder clay for the same kind of sediments, but this has fallen into disfavor. Where it is unclear whether a poorly sorted, unconsolidated glacial deposit was deposited directly from glaciers, it is described as diamict or (when lithified ) as diamictite . Tillite is a sedimentary rock formed by lithification of till. Glacial till is mostly derived from subglacial erosion and from

1640-491: The till. The abundance of clay demonstrates lack of reworking by turbulent flow, which otherwise would winnow the clay. Typically, the distribution of particle sizes shows two peaks (it is bimodal ) with pebbles predominating in the coarser peak. The larger clasts (rock fragments) in till typically show a diverse composition, often including rock types from outcrops hundreds of kilometers away. Some clasts may be rounded, and these are thought to be stream pebbles entrained by

1681-413: The top of the stratigraphic sediment sequence, which has a major influence on land usage. Till is deposited as the terminal moraine , along the lateral and medial moraines and in the ground moraine of a glacier, and moraine is often conflated with till in older writings. Till may also be deposited as drumlins and flutes , though some drumlins consist of a core of stratified sediments with only

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