Hummock

A hummock is a small knoll or mound above ground.[1] They are typically less than 15 meters in height and tend to appear in groups or fields. It is difficult to make generalizations about hummocks because of the diversity in their morphology and sedimentology.[2] An extremely irregular surface may be called hummocky.[3]

An ice hummock is a boss or rounded knoll of ice rising above the general level of an ice-field. Hummocky ice is caused by slow and unequal pressure in the main body of the packed ice, and by unequal structure and temperature at a later period.

Bog hummocks

Hummocks in the shape of low ridges of drier peat moss typically form part of the structure of certain types of raised bog, such as plateau, kermi, palsa or string bog. The hummocks alternate with shallow wet depressions or flarks.

Swamp hummocks

Swamp hummocks are mounds typically initiated as fallen trunks or branches covered with moss and rising above the swamp floor. The low-lying areas between hummocks are called hollows.[4] A related term, used in the Southeastern United States, is "hammock".

Earth hummocks of cryogenic origin

Frost upheaval
Cryogenic earth hummocks on Mount Kenya

Cryogenic earth hummocks go by many different names; in North America they are earth hummocks; thúfur in Greenland and Iceland; and pounus in Fennoscandia. These cold climate landforms appear in regions of permafrost and seasonally frozen ground.[2] They usually develop in fine-grained soils with light to moderate vegetation in areas of low relief where there is adequate moisture to fuel cryogenic processes.[5]

Cryogenic earth hummocks appear in a variety of cold-ground environments, making the story of their genesis complex. Geologists recognize that hummocks may be polygenetic and form by a combination of forces that are yet to be well understood.[2]

Recent research on cryogenic hummocks has focused on their role as environmental indicators. Because hummocks can both form and disintegrate rapidly (well within a human lifetime)[5] they are an ideal landform to monitor for medium range environmental change.[2] There are several explanations of earth hummock formation.

Cryoexpulsion of clasts

Hummocks may form as a result of clasts migrating to the surface through frost push and pull mechanisms. As the clasts rise they push up on the ground above forming bulging mounds.[2]

Cellular circulation

Hummock excavation normally reveals a disturbed soil profile, often with irregular streaks of organic matter or other colorations suggesting fluidity at some time past.[5] The disturbance, a form of cryoturbation often extends to a depth roughly equal to the hummock’s height. This has been explained by some as the result of convection processes whereby warmer soil and water at depth expands, becomes less dense and rises, while gravity forces denser soil downwards. Circulation has also been explained as driven solely by density of soil material, not temperature induced density changes.[3]

Differential frost heave (cryostatic pressure hypothesis)

This is the most widely accepted explanation of cryogenic hummock genesis.[2] Irregularities in preexisting ground conditions (differences in grain size, ground temperature, moisture conditions of vegetation) cause surface downwards freezing during the winter to spread unevenly. Encroaching frost exerted increasing pressure on the adjacent unfrozen soil. Trapped between the freezing surface soils and the buried permafrost layer the soil material is forced upwards into hummocks. While this is currently the most commonly accepted hypothesis, there is still only limited evidence of this happening.[3]

Hummocks created by debris avalanches

Debris avalanches are caused by sudden collapses of large volumes of rock from the flanks of mountains, especially volcanoes.[6] These events are fast-moving, gravity-driven currents of saturated debris that do not necessarily include juvenile material.[7] Debris avalanche deposits are characterized by the debris-avalanche block (hummocks) and the debris-avalanche matrix. Debris avalanches are diagnosed for landscapes where the volcano has an amphitheater at the source with hummocky terrain downhill. In some cases, such as Mount Shasta in California, the amphitheater has been filled in by later volcanic activity and all that remains are the hummocks.[8]

Debris avalanche blocks are identifiable because they keep their internal stratigraphy. The blocks simply break off the mountain and slide down, completely intact, identifiable because they differ from the surrounding landscape.[7] The volume and height of hummocks is mostly dependent on their location; the closer to the source region, the larger they become.[8] The bottom layer of a debris avalanche deposit is the fine-grained matrix which forms due to the shear at the base of the large, turbulent moving mass.[7]

References

  1. ^ Bates, Robert L. and Julia A. Jackson, ed. (1984). “hummock.” Dictionary of Geological Terms, 3rd Ed. New York: Anchor Books. p. 241.
  2. ^ a b c d e f Grab, Stefan. (2003). “Aspects of the geomorphology, genesis and environmental significance of earth hummocks (thufur, pounus): miniature cryogenic mounds.” Progress in Physical Geography 29, 2. p. 139-155.
  3. ^ a b c Willams, Peter J. and Michael W. Smith. (1989). The Frozen Earth: Fundamentals of Geocryology. Cambridge, UK: Cambridge UP, p. 149-163.
  4. ^ http://www.amjbot.org/content/91/8/1251.full
  5. ^ a b c Davis, Neil. (2001). Permafrost: A Guide to Frozen Ground in Transition. Fairbanks, Alaska: University of Alaska Press. p. 133, 137-40, 146, 175-76.
  6. ^ Reubi, O, Ross, P. S., & White, J.D.L. (2005). Debris Avalanche deposits associated with large igneous province volcanism: An example from the Mawson Formation, central Allan Hills, Antarctica. Geological Society of America Bulletin. p. 117, 1612-1627.
  7. ^ a b c Francis, P, & Oppenheimer, C (2003). Volcanoes. Oxford: Oxford University Press.
  8. ^ a b Ui, T., Takarada, S., Yoshimoto, M., (2000). Debris Avalanches. In Sigurdsson, H., Houghton, B.F (eds), Encyclopedia of Volcanoes. San Diego: Academic Press.
  •  This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Hummock". Encyclopædia Britannica (11th ed.). Cambridge University Press.
Barunga Range

The Barunga Range is a range of hills in the northern Mount Lofty Ranges starting near Clements Gap and Merriton in South Australia's Mid North. At the range's southern end it merges with Hummock Range at Barunga Gap, approximately 10 kilometres (6.2 mi) south west of Snowtown. The name 'Barunga' derives from an indigenous term meaning "gap in the range".

The Barunga and Hummock ranges are host to the Clements Gap and Snowtown wind farms.

Black Bog

Black Bog is a raised bog in County Tyrone, Northern Ireland, situated about 17km west of Cookstown. It is one of the two largest intact active bogs in Northern Ireland with hummock and hollow pool complexes and represents one of the best examples of this habitat type in the United Kingdom.

Bundaberg Hummock

The Bundaberg Hummock, also referred to as The Hummock, is an extinct volcano remnant situated in the locality of Qunaba east of Bundaberg, Queensland, Australia. Its official (but rarely used) name is Sloping Hummock. The summit of the hill holds both a memorial to Bert Hinkler and the heritage listed Sir Anthony's Rest

County of Daly

The County of Daly is one of the 49 cadastral counties of South Australia. It was proclaimed in 1862 and named for Governor Dominick Daly. It covers the northern half of Yorke Peninsula stretching just east of the Hummock-Barunga Range in the west and just past the Broughton River in the north.

Humarock

Humarock (often called Humarock Beach or Humarock Island) is part of Scituate, Massachusetts, United States 42°08′10″N 70°41′26″W. Humarock is a picturesque seaside village surrounded by water and situated on Cape Cod Bay midway between Boston and Plymouth. It was separated from the rest of the town in the Portland Gale of 1898 in which the mouth of the North River shifted. Humarock is now accessible from Scituate only by boat or from the Town of Marshfield by bridge.

Hummock Island

Hummock Island is the largest of a group of islands in King George Bay in the Falkland Islands. It has a land area of 3.03 square kilometres (1.17 sq mi) and is about 4.0 miles (6.4 km) long in a north-west to south-east direction. Hummock Island is off the western coast of West Falkland, in a bay that leads to the estuary of the Chartres River. The highest point on the island is in the north-east and is 190 metres (620 ft). There are cliffs which often reach over 60 metres (200 ft) high.Hummock Island is situated between Rabbit Island and Middle Island. Other islands in the Hummock Island group include Green Island and Gid's Island.

In the middle of the Twentieth Century the island was used as an extension of the New Island sheep farm, and heavy grazing caused much of the Tussac grass to be eaten out. This has left areas of bare 'black ground'. However, the present owner has indicated that he will not restock the island but will allow the vegetation to recover. Gid's and Middle Islands are nature reserves.

Hummock Range

The Hummocks or Hummock Range is a range of hills in the northern Mount Lofty Ranges extending north from the eastern edge of Yorke Peninsula in South Australia. It is traversed by the Copper Coast Highway immediately west of where it passes around the northern end of Gulf St Vincent. The Augusta Highway passes to the east of the Hummocks. The Hummock Range includes the settlements of South Hummocks and Kulpara. Towards the range's northern end it continues as the Barunga Range north of Barunga Gap, approximately 10 kilometres (6.2 mi) south west of Snowtown.The Hummocks is a primary source of catchment for Lake Bumbunga near Lochiel.The Hummocks and Barunga ranges are host to the Snowtown wind farm.

Hunter Island (Tasmania)

The Hunter Island, the main island of the Hunter Island Group, is a 7,330-hectare (18,100-acre) island, located in Bass Strait, that lies between King Island and north-west Tasmania, Australia.

The island is located near Three Hummock Island, several kilometres off the north-west coast of Tasmania. The island is run as a cattle property and there is a homestead on the island. A privately owned barge is used for transport to Smithton on the north coast of Tasmania. The island is approximately 25 kilometres (16 mi) long, and 6.5 kilometres (4.0 mi) wide at its widest point.

The East India Ship Phatisalam was wrecked on the island in 1821.

Kitts Hummock, Delaware

Kitts Hummock is an unincorporated community in Kent County, Delaware, United States. Kitts Hummock is located on the Delaware Bay at the end of Kitts Hummock Road southeast of Dover. It was originally named "Kidds Hammock" after 17th Century pirate Captain William Kidd and rumors he buried treasure there. The "Hammock" referred to is the ecological version, meaning a stand of hardwood trees, and the name was inadvertently changed by employees of the Delaware Department of Transportation.Kitts Hummock Beach is an official sanctuary for horseshoe crabs, the state marine animal of Delaware and a "signature species" of the Delaware Bay Estuary.

Mallee Woodlands and Shrublands

Mallee Woodlands and Shrublands (MVG 14) is a Major Vegetation Group which occurs in semi-arid areas of southern Australia. The vegetation is dominated by mallee eucalypts which are rarely over 6 metres high. Other dominant plant genera are Melaleuca, Acacia and Hakea.The composition of the understorey depends on factors such as rainfall, soil composition as well as fire frequency and intensity. In subhumid areas, a variety of grasses and shrubs predominate, while in semi-arid areas hummock grasses (Triodia species) predominate.In 2001, the area covered by this vegetation group was estimated to be 65% of its pre 1788 coverage.The most extensive extant area of this group in Australia today is found in the Great Victoria Desert. Prior to 1788, the largest area occurred in the Murray-Darling basin.The Major Vegetation Subgroups for this group are:

Mallee with hummock grass

Mallee with a dense shrubby understorey

Mallee with an open shrubby understorey

Mallee with a tussock grass understorey.

Moswetuset Hummock

Moswetuset Hummock is a wooded historic place in Quincy, Massachusetts. It was added to the National Register of Historic Places in 1970.The site is located at the northern end of Wollaston Beach along Quincy Bay on East Squantum Street near the junction with Quincy Shore Drive. It was the seat of the ruling Massachusett chief Chickatawbut, who was visited in 1621 by Plymouth Colony commander Myles Standish and Tisquantum (Squanto), a Patuxet guide. Moswetuset means "shaped like an arrowhead".

In his 1747 volume A History of New-England historian Daniel Neal described Moswetuset Hummock as the origin of the name of the indigenous Massachusett tribe, and thus the name of the Commonwealth of Massachusetts:

The Sachem or Sagamore who governed the Indians in this part of the country when the English came hither, had his seat on a small hill, or hummock, containing perhaps an acre and a half, about two leagues to the southward of Boston, which hill or hummock lies in the shape of an Indian's arrowhead, which arrow-heads are called in their language MOS, or MONS, with O nasal, and hill in their language is WETUSET hence, this great sachem's seat was called Moswetuset, which signifies a hill in the shape of an arrow's head, and his subjects, the Moswetuset Indians, from whence with a small variation of the word, the Province received the name MASSACHUSETTS.Hummock is a geological term for a small knoll or mound.

National Register of Historic Places listings in Kent County, Delaware

List of the National Register of Historic Places listings in Kent County, Delaware

This National Park Service list is complete through NPS recent listings posted October 11, 2019.

Contents: Divisions in Delaware

North Point Hummock Light

North Point Light, also known as North Point Hummock Light, was located on North Point, the most northern point on Moreton Island.

North Point Light was constructed in the early 1860s, carrying a large kerosene burner with a reflector.In 1899, the lighthouse was replaced with a hardwood framed structure, clad with corrugated iron. It was the sixth of a group of eight lighthouses in Queensland constructed this way, including, by order of establishment, Little Sea Hill Light, Grassy Hill Light, Goods Island Light, Bay Rock Light, Old Caloundra Light, itself, Gatcombe Head Light and Bulwer Island Light.Oddly, a 1909 listing still describes the light as a square wooden lightroom, carrying a fixed sixth order dioptric apparatus. The light shown is described as a white sector, visible for 7 nautical miles (13 km; 8.1 mi).In 1912 the lighthouse was transferred to the control of the Commonwealth. It was later demolished. The 2010 List of Lights does not list a light at the location.

Qunaba, Queensland

Qunaba is a locality in the Bundaberg Region, Queensland, Australia. In the 2011 census, Qunaba had a population of 822 people.

Rabbit Island, Falkland Islands

Rabbit Island is one of the Falkland Islands in the Hummock Island group. It is near West Falkland, to its west, at the mouth of King George Bay. With a land area of 0.69 square miles (1.78 km2) it is the second largest of the three main islands in the bay, lying 2.8 miles (4.5 km) west of Hummock Island and Middle Island. It is east of the Passage Islands and south east of Split Island.

On three sides the island is roughly rectangular, but there is a long promontory extending to the south-east. The island has very steep slopes up to 61 metres (200 ft) to the north and west, but it slopes gently to the east. The highest points are about 91 metres (299 ft). It was heavily grazed by sheep in the past and there is an old shanty in the valley. Rats have been confirmed on the island.

Three Hummock Island

The Three Hummock Island, part of the Hunter Island Group, is a 70-square-kilometre (27 sq mi) granite island, located in the Bass Strait near King Island, lying off the north-west coast of Tasmania, Australia.The island is named after its three most prominent hills, North, Middle and South Hummock, the latter being the highest with an elevation of 237 metres (778 ft) above mean sea level. Part of the island is a nature reserve, with the rest a pastoral lease where farming took place from the mid-1800s to at least the mid-1970s. The focus of human settlement on the island is the homestead at Chimney Corner at the westernmost point. There is an automated lighthouse at Cape Rochon in the north-east, as well as roads, three airstrips, fencing and a wharf. Seasonal muttonbirding occurs in March and April.

Triodia (plant)

Triodia is a large genus of hummock-forming bunchgrass endemic to Australia. They are known by the common name spinifex, although they are not a part of the coastal genus Spinifex. Many of the soft-leaved members of this species were formerly included in the genus Plectrachne.

Two Hummock Island

Two Hummock Island is an ice-covered island, 9.4 kilometres (6 mi) long in a north-south direction, conspicuous for its two rocky summits Buache Peak and Modev Peak 670 metres (2,198 feet) high, lying 9.6 kilometres (6.0 miles) southeast of Liège Island and 11.5 kilometres (7.1 miles) east of Brabant Island in the Palmer Archipelago. This name has appeared on maps for over 100 years and its usage has become established internationally.

Two Summit Island

Two Summit Island is a small island marked by two prominent summits, lying at the east entrance to Fildes Strait in the South Shetland Islands. It was named initially named Two Hummock Island by DI personnel following their survey in 1935, but this name has been rejected because of probable confusion with Two Hummock Island in the north entrance to Gerlache Strait. Two Summit Island, equally descriptive of the feature, was recommended by the United Kingdom Antarctic Place-Names Committee (UK-APC) in 1954.

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