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40-789: Martin Mere is a mere near Burscough , in Lancashire , England, on the West Lancashire Coastal Plain . The mere is a vast marsh , around grid reference SD 41 15 that was, until it was drained, the largest body of fresh water in England. Martin Mere was formed at the end of the last ice age , when water filled a depression in the glacial drift . Since then its size has varied as water levels have risen and fallen. The original giant lake can be seen on Christopher Saxton 's map from 1579 and stretched from Rufford in

80-515: 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

120-466: 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

160-446: A large surface in proportion to the volume of water it contains. However, there is a limiting depth beyond which a lake does not behave as a mere since the sun does not warm the deeper water and the wind does not mix it. Here, a thermocline develops but where the limiting dimensions lie is influenced by the sunniness and windiness of the site and the murkiness of the water. This last usually depends on how eutrophic (rich in plant nutrients)

200-399: A livelihood for people around. Expressed more technically, the mere consists entirely of the epilimnion . This is quite unlike Windermere where in summer, there is a sharp thermocline at a depth of 9 to 15 metres, well above the maximum depth of 60 metres or so. (M&W p36) At first sight, the defining feature of a mere is its breadth in relation to its shallow depth. This means that it has

240-405: A number of meres. As at Martin Mere in Lancashire , when the fens were being drained to convert the land to pasture and arable agriculture, the meres went too but some are easily traced owing to the characteristic soil. For the reasons given above, it is rich in both calcium carbonate and humus . On the ground, its paleness stands out against the surrounding black, humic soils and on the soil map,

280-434: A thermocline in the short term but where there is a moderately windy climate, the circulation caused by wind drift is sufficient to break this up. (The surface is blown down-wind in a seiche and a return current passes either near the bottom or just above the thermocline if that is present at a sufficient depth.) This means that the bed of the shallow mere is aerated and bottom-feeding fish and wildfowl can survive, providing

320-400: 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

360-510: 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

400-555: Is contrasted against moss (bog) and field against fen. The OED quotation from 1609 does not say what a mere is, except that it looks black. In 1629 mere and marsh were becoming interchangeable but in 1876 mere was "heard, at times, applied to ground permanently under water": in other words, a very shallow lake. The online edition of the OED 's quoted examples relate to: Where land similar to that of Martin Mere, gently undulating glacial till , becomes flooded and develops fen and bog ,

440-417: 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

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480-562: Is recorded in Old English as mere ″sea, lake″, corresponding to They derive from reconstituted Proto-Germanic *mari , itself from Indo-European *mori , the same root as marsh and moor . The Indo-European root *mori gave also birth to similar words in other European languages: Latin mare , ″sea″ (Italian mare , Spanish mar , French mer ); Old Celtic *mori , ″sea″ (Gaulish mori- , more , Irish muir , Welsh môr , Breton mor ); and Old Slavic morje . The word once included

520-705: 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

560-434: Is that they are alongside a river rather than having the river flowing through them. In this way, the mere is replenished by seepage from the bed of the lime-rich river, through the river's natural levée , or by winter floods. The water of the mere is then static through the summer, when the concentration of the calcium carbonate rises until it is precipitated on the bed of the mere. Even quite shallow lake water can develop

600-704: Is used more generally than the English mere. It means "lake", as also seen in the names of lakes containing meer in Northern Germany , e.g. Steinhuder Meer . When the Zuiderzee was enclosed by a dam and its saltwater became fresh, it changed its status from a sea ( zee ) to being known as the IJsselmeer , the lake into which the River IJssel flows. Glacial till Till or glacial till

640-563: 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

680-434: 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

720-683: The " mare 'Wide' vocatum " of Robert of Swaffham's version of the Hereward story ( Chapter XXVI ). If it is, it will have been in existence in the 1070s, when the events of the story took place. Meres similar to those of the English Fens but more numerous and extensive used to exist in the Netherlands , particularly in Holland . See Haarlemmermeer , for example. However, the Dutch word meer

760-539: The Great Levell of the Fenns" of 1720, though Trundle Mere is not named, the above are all named but one, included with the addition of: In the interval, Stretham Mere had gone and the main features of the modern drainage pattern had appeared. Ugg, Ramsey and Benwick meres do not show in the soil map. Others which do but which appear to have been drained before Saxton's mapping in 1576 are at: The last appears to be

800-450: 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

840-498: 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

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880-413: 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

920-577: The east, to Churchtown (then known as North Meols ) in the west. To the north of the lake were the villages of Mere Brow and Holmeswood , the site of Holmeswood Hall, built by the Heskeths as a hunting lodge. South of the lake was the Scarisbrick Hall estate, Martin Hall and Tarlefarwood, now known as Tarlscough . The mere originally drained out in two places; at the western end the arm of

960-529: The former meres show as patches of the Willingham soil association, code number 372 (Soil Map). Apart from those drained in the medieval period, they are shown in Saxton's map of the counties (as they were in his time) of Cambridgeshire and Huntingdonshire. The following is a list of known meres of the eastern English Fenland with their grid references . Saxton's meres are named as: In Jonas Moor's "map of

1000-410: 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

1040-411: 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

1080-401: 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

1120-403: 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

1160-476: The introduction of steam pumping. Farms and market gardens were established on the rich soils of the reclaimed land. Between 1974 and 1982 sand from the former lake bed was quarried for use in glass-making at Mere Sands Wood which is now a nature reserve. An ancient canoe has been excavated from Martin Mere and is on display in the Atkinson Art Gallery and Library . Local legend has it that

1200-537: The lake was home to the nymph Vivian, who stole the knight Lancelot as a child, and brought him up in the depths of the lake's waters. He was also reputed to have been the ruler of Lancashire, the county being named after him. Part of the old mere is now the site of Martin Mere Wetland Centre , a wetland nature reserve managed by the Wildfowl and Wetlands Trust . Mere (lake) The word mere

1240-650: 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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1280-527: The mere known as the Wyke drained into the Pool (or Old Pool) at what is now Crowland Street, Blowick , while at its eastern end it flowed into the river Douglas at Rufford . Active management of the mere began in 1692 when Thomas Fleetwood of Bank Hall cut a channel in an attempt to drain it. Further attempts to drain it were made in the 1780s, but effective drainage was achieved only in the mid-19th century, with

1320-470: 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

1360-442: The remnants of the original mere remain until the whole is filled with peat . This can be delayed where the mere is fed by lime-rich water from chalk or limestone upland and a significant proportion of the outflow from the mere takes the form of evaporation. In these circumstances, the lime (typically calcium carbonate ) is deposited on the peaty bed and inhibits plant growth, therefore, peat formation. A typical feature of these meres

1400-411: The sea or an arm of the sea in its range of meaning but this marine usage is now obsolete ( OED ). It is a poetical or dialect word meaning a sheet of standing water, a lake or a pond ( OED ). The OED 's fourth definition ("A marsh, a fen.") includes wetland such as fen amongst usages of the word which is reflected in the lexicographers' recording of it. In a quotation from the year 598, mere

1440-464: 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

1480-412: 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

1520-491: 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

1560-413: 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

1600-584: The water is. Nonetheless, in general, with the enlargement of the extent of a mere, the depth has to become proportionately less if it is to behave as a mere. There are many examples in Cheshire , including: Many examples also occur in north Shropshire , especially around the town of Ellesmere , which is sometimes known as 'the Shropshire lake district', such as: The Fens of eastern England, as well as fen, lowland moor (bog) and other habitats, included

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