Forms of Relief PDF

# Las formas del relieve The set of shapes that the Earth's surface presents constitutes the relief. These shapes can be grouped into: ## Forms of continental relief * **Mountains**: are elevated terrains with steep slopes. They can be grouped into mountain ranges, systems or chains. The terrains...

# Las formas del relieve The set of shapes that the Earth's surface presents constitutes the relief. These shapes can be grouped into: ## Forms of continental relief * **Mountains**: are elevated terrains with steep slopes. They can be grouped into mountain ranges, systems or chains. The terrains located between the mountains are the valleys and are usually traversed by rivers. * **Plains**: are flat terrains of low altitude. They are located both in coastal areas and in the interior. * **Plateaus**: are flat terrains located at higher altitudes than plains. * **Depressions**: are terrains located at lower altitudes than the lands that surround them, even below sea level. ## Forms of coastal relief The coast or coastline is the contact zone between land and sea. It presents distinct forms: * **Peninsula**: is a piece of land surrounded by water on all sides except for one called an isthmus. * **Island**: is a piece of land surrounded by water on all sides. A group of nearby islands forms an archipelago. * **Cape**: is a part of the coast that extends into the sea. * **Gulf**: is an inlet of the sea into the land. If it is small, it is called a bay. Coves and inlets are even smaller than bays. ## Forms of submarine relief * **Continental shelf**: is a slightly inclined zone that descends to a depth of about 200 meters. It ends at the *continental slope*, which is a zone with a steep slope that leads to great depths. * **Abyssal plain**: extends between 3,000 and 7,000 meters deep. It constitutes the seabed and is usually traversed by *oceanic ridges*, which are large submerged mountain ranges. The peaks of the highest ridges may stick out and form islands. In the abyssal plain, there are also *seamounts*, which are deep and extensive crevices. The deepest one is the Challenger Trench, in the Pacific Ocean, with a depth of over 10,000 meters. # ¿Qué es la teoría de la tectónica de placas? The Earth's surface is always moving in an almost imperceptible way. The effects of this movement are very important. For example, where we now see mountains, millions of years ago there may have been plains; and where we now see emerged lands, there may have been submerged terrains. According to the theory of plate tectonics, the Earth's crust is made up of tectonic plates of different sizes and a few kilometers thick that are constantly moving due to the Earth's internal forces, as if they were puzzle pieces. The plates do not exactly coincide with the continents, as a plate can be made up of both emerged lands and lands submerged under the oceans. In their movement, the plates separate, slide over each other or collide. When they collide, one plate may slide under the other towards the Earth's interior. In other cases, the collision of two plates may lead to the formation of large mountain ranges. In the contact zones of plates, earthquakes or tremors and volcanoes are frequent. # Los volcanes The movement of tectonic plates can cause two more phenomena: volcanoes and tremors. Tectonic tremors are also responsible for the creation and modification of the Earth's relief. Volcanoes are cracks in the Earth's crust through which materials from the Earth's interior are expelled at high temperatures. These cracks are formed by the action of the Earth's internal forces, such as the collision of two plates. Generally, volcanoes are located in the contact zones of tectonic plates. Most volcanic eruptions occur on the seabed. ## Types of Volcanoes Volcanoes can be classified based on their state of activity: * **Active volcanoes** are in permanent activity and enter into eruption every certain period of time. For example, the Popocatépetl in Mexico, recorded several explosions in 2020. * **Dormant or inactive volcanoes** remain inactive for several hundred years, such as Mauna Kea in Hawaii, which last entered into eruption 4,500 years ago. * **Extinct volcanoes** have not shown activity for several thousand years, like Kilimanjaro in Tanzania, whose last eruption took place 360,000 years ago. Volcanic eruptions modify the relief. The expelled material can accumulate on the outside and, when it cools down, form *volcanic cones*, which look like mountains. They can also give rise to islands, such as the Canary Islands or those of the Japanese archipelago. # Los terremotos Earthquakes or tremors are sudden shaking of the Earth's crust caused by the collision of plates, the movements of faults or volcanic eruptions. These jolts spread in all directions in the form of very destructive *seismic waves*. Earthquakes happen constantly, but most are not perceived because they are very mild. The magnitude of an earthquake is measured with *seismographs* and quantified using, normally, the *Richter scale*. The zone with greatest seismic activity is the *Ring of Fire*, a zone that coincides with the edges of the Pacific Ocean. # The action of external forces Relief is constantly changing very slowly due to the action of external forces, such as wind, temperature, water, and living beings. These external processes can be of three types: * **Erosion** is the wear, fragmentation or breakdown of rocks. * **Transport** is the dragging of materials torn off by erosion. * **Sedimentation** is the deposition of eroded and transported materials. ## The wind The wind drags particles of sand and uses them to hit, polish and shape rocks. In addition, the wind transports the sand and deposits it, forming *dunes*. ## Temperature Sudden changes in temperature break rocks into different fragments. This occurs in areas where there are large temperature differences between day and night, such as deserts and mountains. In humid places, water seeps into cracks in the rocks and, when the temperature drops, it freezes, increases its volume and acts like a wedge, breaking the rock. ## Water Water is the main agent that shapes the relief and acts on it in different ways. * **River water**: modifies the relief differently in each section. * **Upper course**: as the slope is very pronounced, the water flows quickly and erodes. That is, it removes materials from the riverbed. The water is so strong that, over millions of years, it can carve deep *canyons* and *gorges*, and narrow *valleys*. * **Middle course**: the river flows through flat areas and at a slower rate. Therefore, it erodes less and transports the materials removed in the previous section. * **Lower course**: the water flows so slowly that it cannot tear off new materials or transport the ones it already carries, which it deposits on the banks. This process is *sedimentation*. Sometimes, this material fills extensive surfaces, forming *alluvial plains*. * **Waves and ocean currents**: shape the coastline, giving rise to *cliffs*, and erode the seabed. They also transport materials and deposit them in other places, creating *beaches*. * **Groundwater**: when it flows through terrains formed by limestone rocks, it dissolves its components and can create caves with unique shapes, such as *stalactites* (which form on the ceiling) and *stalagmites* (which form on the floor). ## Living beings Living beings modify the relief in an important way. For example: * **Plant roots**: can penetrate the soil and break up rocks. * **Some animals**: dig tunnels in the soil and also break up rocks. * **Humans**: deeply transform the landscape by leveling the terrain to build structures and transport routes or to expand farmland; digging tunnels and dams; and mining. # Oceans and seas The oceans and seas form the marine waters, which are salty. Salinity depends on temperature, which is why it is not the same in all seas and oceans. The waters of enclosed and warm seas contain more salt, because heat causes evaporation to be greater than in open and cold seas. ## Oceans Oceans are large bodies of water that surround and separate the continents. There are five oceans on Earth: Atlantic, Arctic Sea, Antarctic Sea, Indian and Pacific. ## Seas Seas are smaller and less deep than oceans, and are located in areas close to the continents. Among the largest seas are the Arabian Sea, the Caribbean Sea and the Mediterranean Sea. # The rivers ## What are Rivers? A river is a continuous current of water that flows in a defined channel from its origin or source to its mouth, where it empties into another river, a lake or the sea. The rivers that flow into another river are called tributaries. The rivers that start in a mountain range and empty into a lake are called torrent rivers. The water of a river flows through a channel, or bed, and the territory that it drains or flows through is called a hydrographic watershed. The rivers that flow into a lake or the sea are all part of the same hydrographic watershed. ## The Riverbed The riverbed is the path that a river travels from its source to its mouth. The riverbed can be divided into three sections: * **Upper course**: usually located in a mountainous area. The water flows rapidly, and the channel is narrow. The water erodes the terrain carving canyons and gorges. Where there is a significant difference in height, waterfalls are formed. * **Middle Course**: the river flows over gentler terrains. The water flows more slowly, causing less erosion. It transports the materials that have been eroded upstream. Large, winding meanders, or bends, in the river channel are formed. * **Lower Course**: the slope is gentle, and the water flows slowly. The weight of the water causes the sediments carried by the river to be deposited along its banks, often filling large areas forming alluvial plains. At the mouth of a river, the water mixes with the water of the sea, forming estuaries. It may also deposit sediments forming triangular areas called deltas. # The lakes Lakes are bodies of water accumulated in a permanent way in the interior of continents, in sunken areas of the ground. They are called lagoons if they are small and inland seas if their water is salty. * Some lakes are fed by rainfall, so their water volume varies with the seasons. Sometimes, lagoons dry up almost completely and swamps form. * In other lakes, the water comes from rivers and underground streams that flow into them or from melting glaciers. In the last twenty years, the largest lakes in the world, such as Baikal, Tanganyika, Victoria and Malawi, have suffered changes as a consequence of global warming, the increase of nutrients in their waters and the introduction of invasive species. # The glaciers Glaciers are masses of ice formed by the accumulation of snow over hundreds of years. They move slowly at a faster or slower rate. When they reach the sea, they break off and form icebergs, which are floating masses of ice. They are located in polar ice caps and on mountain peaks. They are called *alpine glaciers*. They cover 11% of the Earths surface and contain most of the freshwater on the planet. However, they are experiencing the effects of global warming and are expected to lose a large proportion of their volume by 2050 The melting of glaciers in Antarctica is causing sea levels to rise and the waters of the seas to become less salty. # Groundwater Groundwater is the water that is found beneath the Earth's surface. It comes from the rainwater and rivers that seep through the ground until they reach a layer of impermeable rock. It forms underground pools called *aquifers*. Sometimes groundwater comes to the surface through springs (fresh water) or hot springs (hot water). Wells are built to extract it. # The value of the water we cannot see Aquifers hold a large reserve of potable water. They feed rivers and lakes and provide moisture to plants. If they are used abusively and depleted, they take many years to refill. Over the last fifty years, these underground water reserves have been depleted.