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what is a river terrace in geography

by Eve Crist III Published 3 years ago Updated 2 years ago

river terrace

Fluvial terrace

Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a “tread,” separated from either an adjacent floodplain, other fluvial terraces, or uplands by distinctly steeper strips of land called “risers.” These terraces lie parallel to and above the river channel and its floodplain.

, bench or step that extends along the side of a valley and represents a former level of the valley floor. A terrace results from any hydrological or climatic shift that causes renewed downcutting.

river terrace(stream terrace) A fragment of a former valley floor that now stands well above the level of the present flood-plain and is usually covered by fluvial deposits. It is caused by stream incision, which may be caused by uplift of the land, a fall in sea level, or a change in climate.

Full Answer

What is a river terrace called?

River terrace. River terrace, bench or step that extends along the side of a valley and represents a former level of the valley floor. A terrace results from any hydrological or climatic shift that causes renewed downcutting.

What is a terrace in geography?

river terrace, bench or step that extends along the side of a valley and represents a former level of the valley floor. A terrace results from any hydrological or climatic shift that causes renewed downcutting.

What is a river terrace made of?

River terrace. A terrace results from any hydrological or climatic shift that causes renewed downcutting. It generally has a flat top made up of sedimentary deposits and a steep fore edge, and it may be the remains of an old floodplain, cut through by the river and left standing above the present floodplain level.

What is the difference between a river terrace and a floodplain?

The previous floodplain is therefore abandoned and becomes a river terrace. A river terrace is composed of an abandoned surface, or tread, and the incised surface, or riser.

What is the meaning of river terrace?

river terrace, bench or step that extends along the side of a valley and represents a former level of the valley floor. A terrace results from any hydrological or climatic shift that causes renewed downcutting.

How is a river terrace formed?

Stream terraces form when streams carve downward into their floodplains, leaving discontinuous remnants of older floodplain surfaces as step-like benches along the sides of the valley. Stream terraces are common throughout the Western United States.

What does terrace mean in geography?

In geology, a terrace is a step-like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread, that is typically bounded on one side by a steeper ascending slope, which is called a "riser" or "scarp".

Where are river terraces located?

These terraces lie parallel to and above the river channel and its floodplain. Because of the manner in which they form, fluvial terraces are underlain by fluvial sediments of highly variable thickness.

How are terraces formed in geography?

How are Terraces Formed? A terrace can be formed as a river cuts deeper into the land. A new, lower floodplain may then be established, leaving part of the former flood plain at a higher level as a terrace.

How can a river terrace form quizlet?

A rejuvenating river can erode vertically into the former flood plain to produce features called river terraces. 2. When rivers flood on the floodplain, they deposit sediment. Over time this sediment builds up, however due to the erosion of the river, the sediment is cut in two and this forms a river terrace.

What is an example of a terrace?

The definition of a terrace is a patio, balcony or other outdoor living area. An example of a terrace is a paved sitting area which is next to an apartment's back door. To form (a hillside or sloping lawn, for example) into terraces. A narrow strip of landscaped earth in the middle of a street.

Which soil is found on river terraces?

The youngest terrace (Qrt) is called River Terrace (Component 6). The present flood plains (Qra) are called River Flats (rf)....River terraces (Symbol: rt)Surface soilB2175 – 105 cmGreyish brown (10YR5/2); medium clay; weak coarse prismatic structure; firm consistence moist.5 more rows

What is the terrace used for?

Terraces are used primarily for leisure activity such as sitting, strolling, or resting. The term often applies to a raised area in front of a monumental building or structure, which is usually reached by a grand staircase and surrounded by a balustrade.

What creates river terraces or why are floods important ?)?

They can move laterally as a result of bank erosion and deposition, and vertically as a result of bed aggradation or degradation. Floodplains and terraces are usually formed through these processes. Therefore, floodplains and terraces are essentially part of the river system.

Which soil occurs in river terraces above flood level?

Bhangar. The Bhangar is the older alluvium along the river beds forming terraces higher than the flood plain (about 30 metres above the flood level).

What is a stream terrace quizlet?

What is a stream terrace? a remnant of an older floodplain that sits above the stream valley.

What is a river terrace?

A river terrace is a fragment of a former river floodplain that now stands above the level of the present-day floodplain.

What are terraces in a river valley?

Terraces are nearly ubiquitous features of river valleys that attest to a fundamental unsteadiness in the rate of vertical incision. A common source of that unsteadiness is vegetative, geomorphic, and hydrologic response to climate, which for the Quaternary, are characterized by 100-ky glacial-interglacial cycles.

How do river valleys evolve?

River valleys' evolution in mountainous regions, i.e., bottom and lateral erosion, formation of river terraces, etc., depends on the combination of the tectonic and climatic factors mainly. Neotectonic uplifts and subsidences along with water flow characteristics (discharge and its annual variations, annual runoff, and sediment yield) determine the prevalence of erosion or accumulation along the river valley. Tectonic and climatic factors are somehow interrelated, e.g., intensive uplift results in the formation of high mountains subjected to glaciation that change the hydraulic regime of the rivers; increased erosion caused by climate change may intensify isostatic uplift, etc. These interacting processes form a typical shape of river valleys with narrow gorges and steeper thalwegs where they cross actively growing mountain ranges, and widened valleys with well-developed fluvial deposits where they pass through neotectonic depressions.

How is flow competence related to sediment?

The most direct consideration is that of flow competence, which is generally defined as the ability of flowing water to transport sediment of a certain size or caliber, generally determined by a statistical measure of diameter for the largest particles transported. Although mean flow velocity is commonly related to competence, the problem of specifying the actual bed velocity responsible for sediment entrainment causes difficulty in applying competence relationships in relation to velocity. For this reason, competence is more generally expressed in terms of boundary or bed shear stress, which is commonly given in dimensionless terms in order to deal with scaling issues.

What are the main cycles of relief evolution?

The main cycles recognizable in the regional relief evolution are related to the expansion of ice sheets in the Early and Middle Pleistocene. High river terraces and interfluvial areas are mantled with till and glaciofluvial deposits. At the Late Pleistocene beginning (during the Mikulino Interglacial) thick series of lacustrine sediments accumulated in the central and southern part of the region; in the north they gave place to the marine series of the Boreal transgression. Large areas in river valleys are occupied by the first and second river terraces dated to the Late Pleistocene, along with widely spread floodplains. Of older terraces there are only fragments preserved, the corresponding fluvial series being found in the overdeepened segments of the valleys (Fig. 1.7.2 ). Specific features of the river valleys in the Pechora drainage basin made it possible for the Paleolithic communities to migrate over a long distance and to choose the most comfortable dwelling places.

What is the response of a fill terrace?

Fill terraces indicate a response that drives the sediment transport in the channel to range broadly from under-capacity to overcapacity conditions.

How can terraces be used to study the watershed?

Continued advances in and application of numeric dating methods will further permit terrace studies to quantify the timing of terrace formation and better explore the watershed-scale responses to environmental change. Characterizing paleo-erosion rates and precisely when hillslopes liberate sediment during a glacial–interglacial cycle are two examples of how terrace studies will continue to directly influence watershed-scale process investigations. More sophisticated numeric models coupled with field studies dedicated to better understanding the strath formation process remain on the horizon for the next generation of terrace research. As a synthetic and globally applicable genesis model emerges from these studies, fluvial terraces should remain core to a wide range of geologic investigations probing fundamental tectonic, climatic, and paleoclimatic topics.

river terrace

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

River Terrace

one of a series of terraces rising above the floodplain of a river and separated from other terraces by scarps. River terraces are formed during the entrenchment of a river in the flat floor of a valley as a consequence of tectonic uplifts, climatically caused changes in run-off regimes, or the depression of the base level of erosion.

How are river terraces formed?

Origin of river terraces. The treads of river terraces are formed by processes analogous to those that produce floodplains. In depositional terraces, however, the origin of the now abandoned floodplain is much less significant than the long-term episode of valley filling that preceded the final embellishment of the tread.

What is an erosional terrace?

Erosional terraces are those in which lateral river migration and lateral accretion are the dominant processes in constructing the floodplain surface that subsequently becomes the terrace tread.

How does glaciation affect depositional terraces?

An enormous volume of coarse-grained bed load is carried by an active glacier and released at the glacial margin. This influx of sediment simply overwhelms the downstream fluvial system, even though meltwater produced near the ice margin provides greater than normal transporting power to a river emerging from the glacier. As a result, valley reaches downstream from the ice margin begin to fill with coarse debris (outwash), which cannot be transported on the channel gradient that existed prior to the glacial event. Deposition ensues, and the valley aggrades until the gradient, load, and discharge conditions are modified enough to allow transport of the entire load or to initiate river entrenchment into the fill.

Where are rock cut terraces found?

Rock-cut terraces were first and best described in the Big Horn Basin of Wyoming, although some of the terraces in that area may be depositional in origin.

Is terrace formation synchronous?

Deposition and entrenchment involved in terrace formation is clearly not synchronous along the entire length of such a river system. In addition, it is now known that more than one terrace can result during a period of entrenchment.

What is a terrace?

For other uses, see Terrace (disambiguation). In geology, a terrace is a step-like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread, that is typically bounded on one side by a steeper ascending slope, which is called a "riser" or "scarp". The tread and the steeper descending slope (riser or scarp) ...

What is a fluvial terrace?

Fluvial terraces are remnants of the former floodplain of a stream or river. They are formed by the downcutting of a river or stream channel into and the abandonment and lateral erosion of its former floodplain.

What are the terraces of ancient ice-walled lakes?

In case of the lake terraces of ancient ice-walled lakes, some proglacial lakes, and alluvium-dammed (slackwater) lakes, they often represent the relict bottom of these lakes. Finally, glaciolacustrine kame terraces are either the relict deltas or bottoms of ancient ice marginal lakes.

What is a narrow terrace called?

A narrow terrace is often called a bench. The sediments underlying the tread and riser of a terrace are also commonly, but incorrectly, called terraces, leading to confusion. Terraces are formed in various ways.

How do marine terraces form?

The formation of a marine terrace follows this general process: A wave cut platform must be carved into bedrock (high wa ve energy is needed for this process). Although this is the first step to the process for the formation of a marine terrace, not all wave cut platforms will become a marine terrace. After the wave cut platform is formed it must be removed from interaction with the high wave energy. This process happens by either change in sea level due to glacial-interglacial cycles or tectonically rising landmasses. When the wave cut has been raised above sea level it is preserved. The terraces are most commonly preserved in flights along the coastline.

Where are Kame terraces formed?

Kame terraces are formed on the side of a glacial valley and are the deposits of meltwater streams flowing between the ice and the adjacent valley side.

What is a raised shoreline?

Raised shoreline – An ancient shoreline exposed above current water level. Terrace (earthworks) Wave-cut platform – The narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion.

What is a marine terrace?

A marine terrace is any relatively flat surface of marine origin, bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side. Marine terraces may result from marine abrasion or denudation (marine-cut terraces, or shore platforms, see Figure 5 ), or consist of shallow water to slightly emerged accumulations of materials removed by shore erosion (marine-built terraces), or also have a polygenic origin, with occurrence of in situ deposits after an abrasion phase ( Figure 11 ).

Why are there stepped terraces?

The occurrence of a series of stepped marine terraces usually results from eustatic changes in sea level superimposed on a tectonic trend . Uplifted terraces that act as a continuous tape recorder, each step developing when the rising sea level overtakes the rising land, may be most useful for Quaternary environmental studies, since each terrace can be considered as a fossil counterpart of the present-day terrace, platform, or reef flat. In seismic areas, however, terrace steps may have a tectonic origin ( Figure 13 ).

How to tell the age of a Pleistocene terrace?

The age of a Pleistocene terrace is generally deduced from radiometric dating of marine organisms collected in growth position. U-Series and electron spin resonance (ESR) are the most frequently used dating methods for Pleistocene marine terraces, and radiocarbon for Postglacial and Holocene terraces. From a geomorphologic point of view, the best sea-level indicator of a terrace is the limit between the upper part of the terrace and the adjacent cliff base, especially if it is marked by a notch, because it can be correlated with the peak of the corresponding eustatic transgression. Its accuracy as sea-level indicator depends on the local tidal range and exposure to wave action.

What is the best sea level indicator of a terrace?

From a geomorphologic point of view, the best sea-level indicator of a terrace is the limit between the upper part of the terrace and the adjacent cliff base , especially if it is marked by a notch, because it can be correlated with the peak of the corresponding eustatic transgression.

What are marine deposits left in uplifting regions by a tsunami?

Marine deposits left in uplifting regions by a tsunami (like the tsunami produced 7.1 radiocarbon ka by the Storegga Slide on Northern Europe coasts) may provide accurate stratigraphical indicators, enabling the estimate of the change in the relative sea level since the tsunami event ( Smith et al., 2004 ).

Why are terraces chalky?

The fossils from non-cemented terraces can offer a chalky appearance because of weathering. In any case over a long time period water circulation (contamination?) was produced.

When the uplift rate is sufficiently rapid, each major marine terrace may correspond to a different interglacial period or?

When the uplift rate is sufficiently rapid (>1 mm year −1 ), each major marine terrace may correspond to a different interglacial period or stage. In this case, ages increase with elevation, the upper levels also being the less well preserved. For slower uplift rates, major marine terraces may have a polycyclic origin, with sea level coming back at the terrace level after a period of exposure to weathering.

Which river valley has a lot of fluvial terraces?

Older floodplains and river valleys can have many fluvial terraces. The Rhine Valley of Central Europe, for instance, has dozens of fluvial terraces created by the meandering Rhine as well as intense glaciation. Fluvial terraces in the Rhine allow geologist s to examine more than 100,000 years of Europe’s past.

How does a river erode a floodplain?

A river erodes a floodplain as it meanders, or curves from side to side. The massive lowland floodplain of the Amazon River, for instance, is carved with hundreds of oxbow lake s that document the meandering river and its tributaries over time.

What are the two processes that occur in the natural development of floodplains?

The erosion of a floodplain describes the process in which earth is worn away by the movement of a floodway. Aggradation (or alluviation) of a floodplain describes the process in which earthen material increases as the floodway deposits sediment.

How big is the flood fringe of the Todd River?

The flood fringe of the seasonal Todd River extends the floodplain to 445 square kilometers (170 square miles). Some floodplains are extraordinarily wide. The Barotse floodplain of the Zambezi River, for example, is a vast wetland stretching thousands of kilometers through Angola, Zambia, and Botswana.

Is the Todd River a seasonal floodway?

Floodways can sometimes be seasonal, meaning the channel is dry for part of the year. The floodway of the Todd River in Australia’s Northern Territory, for instance, is an ephemeral stream, meaning its channel can be dry for months at a time. Beyond the floodway is the flood fringe.

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Overview

River terrace formation

Long-lived river (fluvial) systems can produce a series of terrace surfaces over the course of their geologic lifetime. When rivers flood, sediment deposits in sheets across the floodplain and build up over time. Later, during a time of river erosion, this sediment is cut into, or incised, by the river and flushed downstream. The previous floodplain is therefore abandoned and becomes a r…

Climate and terraces

Rivers in continental interiors that have not experienced tectonic activity in the geological recent history likely record climatic changes through terracing. Terraces record natural, periodic variations driven by cycles such as the Milankovitch cycle. These cycles can describe how the Earth's orbit and rotational wobble vary over time. The Milankovitch cycles, along with solar forc…

Tectonic uplift and terraces

In contrast, coastal marine terraces can be preserved only by tectonism or a progressive lowering of sea level. The seismically active coastline of southern California, USA, for example, can be considered an emergent coastline, where tectonism due to transpression provides uplift of shorelines formed during periods of relatively high sea level. Subsequent wave erosion along uplifted portions of the coastline produces an inset wave cut platform and terrace riser below th…

Tectonic–climatic interactions and terraces

Tectonic uplift and climatic factors interact as a positive feedback system, where each forcing mechanism drives the other. One of the greatest examples of this feedback between tectonic and climatic interactions may be preserved in the Himalayan front and in the development of the rain shadow effect and the Asian Monsoon.
The Himalayas act as an orographic barrier that can impede atmospheric circulation and moving a…

See also

• Tectonic–climatic interaction

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