Category Earth Science

Erosion is the wearing away of rocks and other matter on the Earth’s surface by a natural force, such as a sliding glaciers, a flowing river, or the wind. Material that is rubbed off is carried away and deposited somewhere else.

Most erosion is performed by liquid water, wind, or ice (usually in the form of a glacier). If the wind is dusty, or water or glacial ice is muddy, erosion is taking place. The brown color indicates that bits of rock and soil are suspended in the fluid (air or water) and being transported from one place to another. This transported material is called sediment.

Water erosion

This is caused by falling rain or flowing water. Rivers, for example, wear away the land that they flow over, changing the surrounding landscape. Raindrops hit bare soil with enough force to break the soil aggregates. These fragments wash into soil pores and prevent water from infiltrating the soil. Water then accumulates on the surface and increases runoff which takes soil with it.

Well-structured soils are less prone to break up, and the impact of raindrops is minimized if the soil surface is protected by plant or litter cover. 

Wind erosion

The force of the wind can remove pieces of rock and carry them off. Wind erosion is common in deserts. Wind erosion is a serious environmental problem attracting the attention of many across the globe. It is a common phenomenon occurring mostly in flat, bare areas; dry, sandy soils; or anywhere the soil is loose, dry, and finely granulated. Wind erosion damages land and natural vegetation by removing soil from one place and depositing it in another. It causes soil loss, dryness and deterioration of soil structure, nutrient and productivity losses and air pollution. Suspended dust and dirt is inevitably deposited over everything. It blows on and inside homes, covers roads and highways, and smothers crops. Sediment transport and deposition are significant factors in the geological changes which occur on the land around us and over long periods of time are important in the soil formation process.

Ice erosion

As glaciers move, they rub away the land under them, carrying the broken-down material with them. Ice erosion occurs in one of two forms, the movement of glaciers, or thawing processes. In the latter formation, water inside pores and rock fractures expand, which causes further cracking. Glaciers erode through one of three different processes, including abrasion, plucking, and thrusting. Debris caught in the basal brushes along the bed, which polishes and gouges the rocks underneath. Glaciers also cause bedrock to fall off during the plucking phase. In addition, glaciers freeze and then move forward, which dislodges the sediments at the glacier’s base. The latter method produces thousands of lake basins that lie across the edge of the Canadian Shield. All of these combined processes form moraines, drumlins, kames, moulins, and glacial erratics, especially at the glacier retreat.

Extreme cold weather temperatures cause trapped water particles to expand in its cracks, which breaks the rock into several pieces. This senior care leads to gravity erosion, particularly on steep slopes, and the formation of scree at the bottom of a mountainside. Morning thaws can present structural problems for roads alongside mountain cliffs. Additionally, trapped water in the wedge of a rock causes fissures, which eventually breaks down the rock.

Coastal erosion

Crashing waves gradually wear away the rock in cliffs, and sweep up material from the beach. Coastal erosion is typically driven by the action of waves and currents, but also by mass wasting processes on slopes, and subsidence (particularly on muddy coasts). Significant episodes of coastal erosion are often associated with extreme weather events (coastal storms, surge and flooding) but also from tsunami, both because the waves and currents tend to have greater intensity and because the associated storm surge or tsunami inundation can allow waves and currents to attack landforms which are normally out of their reach. On coastal headlands, such processes can lead to undercutting of cliffs and steep slopes and contribute to mass wasting. In addition, heavy rainfall can enhance the saturation of soils, with high saturation leading to a reduction in the soil’s shear strength, and a corresponding increase in the chance of slope failure (landslides).

Coastal erosion is a natural process which occurs whenever the transport of material away from the shoreline is not balanced by new material being deposited onto the shoreline. Many coastal landforms naturally undergo quasi-periodic cycles of erosion and accretion on time-scales of days to years. This is especially evident on sandy landforms such as beaches, dunes, and intermittently closed and open lagoon entrances. However, human activities can also strongly influence the propensity of landforms to erode.

 

Picture Credit : Google

The glacier terminus is the lower end of a glacier. it is sometimes called the toe or snout. Some glaciers end further down a mountain, where the ice melts to form lakes and streams. Others reach the coast, where large chunks break off into the sea, creating icebergs. This is called calving.

Tracking the change in location of a glacier terminus is a method of monitoring a glacier’s movement. The end of the glacier terminus is measured from a fixed position in neighboring bedrock periodically over time. The difference in location of a glacier terminus as measured from this fixed position at different time intervals provides a record of the glacier’s change. A similar way of tracking glacier change is comparing photographs of the glacier’s position at different times.

The form of a glacier terminus is determined by many factors. If the glacier is retreating, it is usually mildly sloping in form because a melting glacier tends to assume this shape. But there are many conditions that alter this typical shape, including the presence of thermal fields and various stresses that cause cracking and melting feedback resulting in glacial calving and other diverse forms.

 

Picture Credit : Google

Cirques 

Cirques are deep hollows near the top of a glacier, formed where a glacier has moved over an area and worn away the rock. The glacial cirque is opened on the downhill side while the cupped section is steep. The cliffs on the sides slope down and combine and converge from three or more higher sides. The floor of the cirque is bowl-shaped because of the convergence zones of combining ice flows from a different direction and the debris accompanying them. A Cirque experiences greater erosion because of the accompanying rock burdens which may also over deepen the level of a cirque. Cirques subjected to seasonal melting often form small lakes called tarns behind the Moraine.

Accumulation zones 

Accumulation Zones are found at the top of glaciers, where the snowfall has built up, often over hundreds of years. Glaciologists subdivide glaciers into glacier accumulation zones, based on the melting and refreezing occurring. These zones include the dry snow zone, in which the ice entirely retains subfreezing temperatures and no melting occurs. Dry snow zones only occur within the interior regions of the Greenland and Antarctica ice sheets. Below the dry snow zone is the percolation zone, where some melt water penetrates down into the glacier where it refreezes. In the wet snow zone, all the seasonal snow melts. The melt water either percolates into the depths of the glacier or flows down-glacier where it might refreeze as superimposed ice. A glacier’s equilibrium line is located at the lower limit of the wet snow zone.

Valley glaciers 

Valley glaciers flow through steep-walled valleys. They eventually wear down the valley sides, making them much rounder. Valley glaciers that flow far enough to reach the sea are called tidewater glaciers. Such glaciers are often the source of numerous small icebergs that might pose a problem to navigating vehicles. Often fjords are formed at the edges of such glaciers when the glaciers retreat and sea water fills the void. A hanging glacier is a part of a valley glacier system. Such glaciers originate high on a glacial valley’s walls and descend to a certain extent along the valley before making an abrupt stop, usually at a cliff. Such glaciers are called hanging glaciers and ice fall and avalanches originating at such glaciers are responsible for snow and ice on the valley floor lying below. When such hanging glaciers retreat, hanging valleys are formed. The Mer de Glace glacier on the Mont Blanc massif’s northern slopes is a valley glacier in the French Alps.

Lateral moraines 

Lateral moraines are long ridges of rock, soil, and dirt left along the sides of a moving glacier. They form only in the ablation zone of a glacier (where more ice is melting than is accumulating as snow each year). This makes them good indicators of where the line between the accumulation zone and the ablation zone—the equilibrium line—occurred on past glaciers. They often remain on the landscape long after glacier retreat and are frequently contiguous with terminal moraines.

Medical moraines 

A medial moraine is found on top of and inside an existing glacier. Medial moraines are formed when two glaciers meet. Two lateral moraines from the different glaciers are pushed together. This material forms one line of rocks and dirt in the middle of the new, bigger glacier. 

If a glacier melts, the medial moraine it leaves behind will be a long ridge of earth in the middle of a valley.

A glacier is a huge river of ice that forms when thick layers of snow fall on top of each other and are pressed together. Most glaciers form high up in mountains, where it’s so cold that any snowfall never melts. They are found all around the world, usually in polar and mountainous regions.

Most of the world’s glacial ice is found in Antarctica and Greenland, but glaciers are found on nearly every continent, even Africa. Because certain climatic and geographic conditions must be present for glaciers to exist, they are most commonly found above snow line: regions of high snowfall in winter and cool temperatures in summer. This condition allows more snow to accumulate on the glacier in the winter than will melt from it in the summer. This is why most glaciers are found either in mountainous areas or the Polar Regions. However, snow line occurs at different altitudes: in Washington State the snow line is around 1,600 meters (5,500 feet), while in Africa it is over 5,100 meters (16,732 feet), and in Antarctica it is at sea level. The amount of snowfall a glacier receives is very important to its survival, which is why some cold regions, like Siberia, have almost no glaciation—there is not enough snowfall.

 

Picture Credit : Google

Near the sea, salt water mixes with fresh water, forming an estuary. The land is flatter, so the river slows down. If it slows down enough, mud is deposited, creating a delta with several channels that the river now flows through.

The basic difference between estuary and delta is that the former is a tidal mouth of the river, where it meets the sea, whereas the latter is nothing but the wetland, formed as a result of the accumulation of sediments carried by the river when it joins a standing water body.

While an estuary is a semi-enclosed body of water, where river meets the ocean, the delta is a low-lying plain, formed by the accumulation of alluvium. There is four major types of estuaries which are drowned river valley estuary, bar-built estuary, fjord estuary and tectonic estuary. On the contrary, various types of delta include wave-dominated delta, tide-dominated delta, Gilbert delta, tidal-freshwater delta, inland delta and mega-delta.

 

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These are flat areas of land next to a river. Water in river may increase for some reason and become too much for the river to carry. It then overflows onto the floodplain. Soil in floodplains is usually very fertile.

A flood plain consists of two parts. The first is the main channel of the river itself, called the floodway. Floodways can sometimes be seasonal, meaning the channel is dry for part of the year. 

Beyond the floodway is the flood fringe. The flood fringe extends from the outer banks of the floodway to the bluff lines of a river valley. Bluff lines, also called valley walls, mark the area where the valley floor begins to rise into bluffs.

Some rivers have very narrow flood plains. In fact, some rivers, or parts of rivers, seem to have no flood plain at all. These rivers usually have a steep stream gradient—a very deep, fast-moving channel. 

 

Picture Credit : Google