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40-624: The Tikitere Graben is a intra-rift graben in the North Island of New Zealand that contains the Ohau Channel , which drains Lake Rotorua into Lake Rotoiti with a minimal drop between the lakes. The Ohau Channel ultimately allows both lakes to drain into the Kaituna River through drainage that is also associated with the graben. The Tikitere Graben also is associated with the geothermal tourist attraction of Hell's Gate and

80-414: A broader floodplain may result. Deposition dominates over erosion. A typical river basin or drainage basin will incorporate each of these different types of valleys. Some sections of a stream or river valleys may have vertically incised their course to such an extent that the valley they occupy is best described as a gorge , ravine , or canyon . Rapid down-cutting may result from localized uplift of

120-533: A cirque glacier. During glacial periods, for example, the Pleistocene ice ages, it is in these locations that glaciers initially form and then, as the ice age proceeds, extend downhill through valleys that have previously been shaped by water rather than ice. Abrasion by rock material embedded within the moving glacial ice causes the widening and deepening of the valley to produce the characteristic U or trough shape with relatively steep, even vertical sides and

160-594: A narrow valley with steep sides. Gill is used to describe a ravine containing a mountain stream in Cumbria and the Pennines . The term combe (also encountered as coombe ) is widespread in southern England and describes a short valley set into a hillside. Other terms for small valleys such as hope, dean, slade, slack and bottom are commonly encountered in place-names in various parts of England but are no longer in general use as synonyms for valley . The term vale

200-432: A relatively flat bottom. Interlocking spurs associated with the development of river valleys are preferentially eroded to produce truncated spurs , typical of glaciated mountain landscapes. The upper end of the trough below the ice-contributing cirques may be a trough-end . Valley steps (or 'rock steps') can result from differing erosion rates due to both the nature of the bedrock (hardness and jointing for example) and

240-465: A slower rate than that of the main valley floor; thus the difference in the two valleys' depth increases over time. The tributary valley, composed of more resistant rock, then hangs over the main valley. Trough-shaped valleys also form in regions of heavy topographic denudation . By contrast with glacial U-shaped valleys, there is less downward and sideways erosion. The severe downslope denudation results in gently sloping valley sides; their transition to

280-427: A valley between its sides is referred to as the valley floor. The valley floor is typically formed by river sediments and may have fluvial terraces . The development of a river valley is affected by the character of the bedrock over which the river or stream flows, the elevational difference between its top and bottom, and indeed the climate. Typically the flow will increase downstream and the gradient will decrease. In

320-510: A variety of transitional forms between V-, U- and plain valleys can form. The floor or bottom of these valleys can be broad or narrow, but all valleys have a shoulder. The broader a mountain valley, the lower its shoulders are located in most cases. An important exception is canyons where the shoulder almost is near the top of the valley's slope. In the Alps – e.g. the Tyrolean Inn valley –

360-561: A very young Kaituna River gorge and a possible route far to the east beyound the present eastern end of Lake Rotoiti is suspected. It is known that after the Rotoiti eruption Lake Rotorua rose to an elevation of just over 370 m (1,210 ft) and at a later stage drained through the Tikitere Graben back into what is now Lake Rotoiti scoring an approximately 1 km (0.62 mi) wide, 60 m (200 ft) deep channel in

400-405: Is a tributary valley that is higher than the main valley. They are most commonly associated with U-shaped valleys, where a tributary glacier flows into a glacier of larger volume. The main glacier erodes a deep U-shaped valley with nearly vertical sides, while the tributary glacier, with a smaller volume of ice, makes a shallower U-shaped valley. Since the surfaces of the glaciers were originally at

440-405: Is either graben or grabens . A graben is a valley with a distinct escarpment on each side caused by the displacement of a block of land downward. Graben often occur side by side with horsts . Horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of

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480-531: Is not known, but would have been through the Tikitere Graben most of the time since. The outlet was perhaps initially through the Hemo Gap to the south of the present town of Rotorua. Whatever there has been drainage at times through the Hemo Gap, and at some stage drainage of Rotorua Lake through the Tikitere Graben became established prior to the Rotoiti eruption in the Ōkataina Volcanic Centre of 47,400 years ago. Drainage may not have been through what seems to be

520-501: Is only 50 meters (160 ft) deep while the main fjord is around 1,300 meters (4,300 ft) at the same point. Glaciated terrain is not the only site of hanging streams and valleys. Hanging valleys are also simply the product of varying rates of erosion of the main valley and the tributary valleys. The varying rates of erosion are associated with the composition of the adjacent rocks in the different valley locations. The tributary valleys are eroded and deepened by glaciers or erosion at

560-544: Is subsiding at 0.2 cm/year (0.079 in/year) and has destroyed the Rotorua Caldera rim at this point, so providing the current natural outlet for Lake Rotorua. The graben is a tectonic intra-rift graben within the Taupo Rift and is delimited by two unnamed active faults in the current active NZ fault database (#3590 and #2210). These north-west to south-east trending faults could be modelled to suggest

600-488: Is the word cwm borrowed from Welsh . The word dale occurs widely in place names in the north of England and, to a lesser extent, in southern Scotland. As a generic name for a type of valley, the term typically refers to a wide valley, though there are many much smaller stream valleys within the Yorkshire Dales which are named "(specific name) Dale". Clough is a word in common use in northern England for

640-629: Is used in England and Wales to describe a wide river valley, usually with a particularly wide flood plain or flat valley bottom. In Southern England, vales commonly occur between the outcrops of different relatively erosion-resistant rock formations, where less resistant rock, often claystone has been eroded. An example is the Vale of White Horse in Oxfordshire. Some of the first human complex societies originated in river valleys, such as that of

680-504: The Nile , Tigris-Euphrates , Indus , Ganges , Yangtze , Yellow River , Mississippi , and arguably the Amazon . In prehistory , the rivers were used as a source of fresh water and food (fish and game), as well as a place to wash and a sewer. The proximity of water moderated temperature extremes and provided a source for irrigation , stimulating the development of agriculture . Most of

720-668: The first civilizations developed from these river valley communities. Siting of settlements within valleys is influenced by many factors, including the need to avoid flooding and the location of river crossing points. Numerous elongate depressions have been identified on the surface of Mars , Venus , the Moon , and other planets and their satellites and are known as valles (singular: 'vallis'). Deeper valleys with steeper sides (akin to canyons) on certain of these bodies are known as chasmata (singular: 'chasma'). Long narrow depressions are referred to as fossae (singular: 'fossa'). These are

760-463: The footwall is upward. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between graben; the bounding faults of a horst typically dip away from the center line of the horst. Single or multiple graben can produce a rift valley . In many rifts , the graben are asymmetric, with a major fault along only one of the boundaries, and these are known as half-graben. The polarity (throw direction) of

800-530: The Kaituna River. The wall meet its design parameters. As of 2020, because of perhaps this measure amongst others, there is stable water quality in Lake Rotoiti. The Ohau Channel itself is regularly monitored for fish biodiversity with reducing abundance of the common bully in the period between 2007 and 2012. This continued into 2016 with changes observed in other river fish. The Tikitere Graben

840-524: The Scandinavian ice sheet during the various ice ages advanced slightly uphill against the lie of the land. As a result, its meltwaters flowed parallel to the ice margin to reach the North Sea basin, forming huge, flat valleys known as Urstromtäler . Unlike the other forms of glacial valleys, these were formed by glacial meltwaters. Depending on the topography , the rock types , and the climate ,

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880-511: The actual valley bottom is unclear. Trough-shaped valleys occur mainly in periglacial regions and in tropical regions of variable wetness. Both climates are dominated by heavy denudation. Box valleys have wide, relatively level floors and steep sides. They are common in periglacial areas and occur in mid-latitudes, but also occur in tropical and arid regions. Rift valleys, such as the Albertine Rift and Gregory Rift are formed by

920-612: The expansion of the Earth 's crust due to tectonic activity beneath the Earth's surface. There are many terms used for different sorts of valleys. They include: Similar geographical features such as gullies , chines , and kloofs , are not usually referred to as valleys. The terms corrie , glen , and strath are all Anglicisations of Gaelic terms and are commonly encountered in place-names in Scotland and other areas where Gaelic

960-443: The flow slower and both erosion and deposition may take place. More lateral erosion takes place in the middle section of a river's course, as strong currents on the outside of its curve erode the bank. Conversely, deposition may take place on the inside of curves where the current is much slacker, the process leading to the river assuming a meandering character. In the lower valley, gradients are lowest, meanders may be much broader and

1000-413: The graben is being produced by a transtensional stress regime or as an accommodation zone between offset spreading centres. Historically some suspect that the graben did not exist, after the Rotorua Caldera forming Mamaku eruption of approximately 240,000 years ago. After this, the lake filled to a maximum elevation of 414 m (1,358 ft) above sea level. The drainage of this initial Lake Rotorua

1040-427: The land surface or rejuvenation of the watercourse as a result for example of a reduction in the base level to which the river is eroded, e.g. lowered global sea level during an ice age . Such rejuvenation may also result in the production of river terraces . There are various forms of valleys associated with glaciation. True glacial valleys are those that have been cut by a glacier which may or may not still occupy

1080-419: The main bounding faults typically alternates along the length of the rift. The asymmetry of a half-graben strongly affects syntectonic deposition. Comparatively little sediment enters the half-graben across the main bounding fault because of footwall uplift on the drainage systems. The exception is at any major offset in the bounding fault, where a relay ramp may provide an important sediment input point. Most of

1120-415: The near common outlet level of today's 280 m (920 ft). Graben In geology , a graben ( / ˈ ɡ r ɑː b ən / ) is a depressed block of the crust of a planet or moon, bordered by parallel normal faults . Graben is a loan word from German , meaning 'ditch' or 'trench'. The first known usage of the word in the geologic context was by Eduard Suess in 1883. The plural form

1160-463: The ocean or perhaps an internal drainage basin . In polar areas and at high altitudes, valleys may be eroded by glaciers ; these typically have a U-shaped profile in cross-section, in contrast to river valleys, which tend to have a V-shaped profile. Other valleys may arise principally through tectonic processes such as rifting . All three processes can contribute to the development of a valley over geological time. The flat (or relatively flat) portion of

1200-436: The power of the moving ice. In places, a rock basin may be excavated which may later be filled with water to form a ribbon lake or else by sediments. Such features are found in coastal areas as fjords . The shape of the valley which results from all of these influences may only become visible upon the recession of the glacier that forms it. A river or stream may remain in the valley; if it is smaller than one would expect given

1240-446: The same elevation , the shallower valley appears to be 'hanging' above the main valley. Often, waterfalls form at or near the outlet of the upper valley. Hanging valleys also occur in fjord systems underwater. The branches of Sognefjord are much shallower than the main fjord. The mouth of Fjærlandsfjord is about 400 meters (1,300 ft) deep while the main fjord nearby is 1,200 meters (3,900 ft) deep. The mouth of Ikjefjord

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1280-499: The sediment will enter the half-graben down the unfaulted hanging wall side (e.g., Lake Baikal ). Valley At lower latitudes and altitudes, these glacially formed valleys may have been created or enlarged during ice ages but now are ice-free and occupied by streams or rivers. In desert areas, valleys may be entirely dry or carry a watercourse only rarely. In areas of limestone bedrock , dry valleys may also result from drainage now taking place underground rather than at

1320-550: The shoulders are quite low (100–200 meters above the bottom). Many villages are located here (esp. on the sunny side) because the climate is very mild: even in winter when the valley's floor is filled with fog, these villages are in sunshine . In some stress-tectonic regions of the Rocky Mountains or the Alps (e.g. Salzburg ), the side valleys are parallel to each other, and are hanging . Smaller streams flow into rivers as deep canyons or waterfalls . A hanging valley

1360-849: The size of its valley, it can be considered an example of a misfit stream . Other interesting glacially carved valleys include: A tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. Such valleys can be up to 100 km (62 mi) long, 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep (its depth may vary along its length). Tunnel valleys were formed by subglacial water erosion . They once served as subglacial drainage pathways carrying large volumes of meltwater. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion. In northern Central Europe,

1400-520: The surface. Rift valleys arise principally from earth movements , rather than erosion. Many different types of valleys are described by geographers, using terms that may be global in use or else applied only locally. Valleys may arise through several different processes. Most commonly, they arise from erosion over long periods by moving water and are known as river valleys. Typically small valleys containing streams feed into larger valleys which in turn feed into larger valleys again, eventually reaching

1440-407: The upper valley, the stream will most effectively erode its bed through corrasion to produce a steep-sided V-shaped valley. The presence of more resistant rock bands, of geological faults , fractures , and folds may determine the course of the stream and result in a twisting course with interlocking spurs . In the middle valley, as numerous streams have coalesced, the valley is typically wider,

1480-407: The valley at the present day. Such valleys may also be known as glacial troughs. They typically have a U-shaped cross-section and are characteristic landforms of mountain areas where glaciation has occurred or continues to take place. The uppermost part of a glacial valley frequently consists of one or more 'armchair-shaped' hollows, or ' cirques ', excavated by the rotational movement downslope of

1520-525: The western arm of Lake Rotoiti to reach initially the eastern Rotoiti craters of the Haroharo caldera in the Ōkataina Volcanic Centre and then on to the sea. By about 9500 years ago dome building activity in the eastern Haroharo portions of the Ōkataina Volcanic Centre had raised Lake Rotoiti to a maximum elevation of 294 m (965 ft) so it started flowing down the Kaituna River and in due course further graben sinking resulted in both lakes having

1560-554: The western aspects of Lake Rotoiti. From the 1950's onward the water quality of Lake Rotoiti deteriorated due to drainage into the lake via the Ohau Channel of water from Lake Rotorua that had high phytoplankton and nutrient concentrations. In July 2008 a wall was completed that directed the outflow of the Ohau Channel towards the Okere Arm in Lake Rotoiti, with the aim of reducing water mixing in Lake Rotoiti before outflow into

1600-414: Was once widespread. Strath signifies a wide valley between hills, the floor of which is either level or slopes gently. A glen is a river valley which is steeper and narrower than a strath. A corrie is a basin-shaped hollow in a mountain. Each of these terms also occurs in parts of the world formerly colonized by Britain . Corrie is used more widely by geographers as a synonym for (glacial) cirque , as

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