Following is a continuation of the notes posted last week on Land forms on Earth. Here’s the link to the previous notes, which contains details on the Major Landforms, in case you missed: Landforms on Earth Part 1.
The following article contains the characteristics and types of major landforms as well as minor landforms.
Types and Characteristics of Major Landforms:
Mountain landforms cover approximately 1/5th of the Earth’s surface. Around 80% of world’s fresh water comes from the mountains. The characteristics of Mountain landforms vary depending on their location, altitude, biomes and the body of water that surrounds them, and their distance from the equator.
There are a few features which are common in all mountains:
- Higher elevation than the surrounding areas
- Have steep slopes, sharp/rounded ridges and a peak/summit
- They’re formed by volcanic or tectonic activities
- High relief within the mountain ranges
Mountain landforms experience higher precipitation than other ecosystems. The weather on mountains varies according to the location and altitude. The weather on mountains is also highly unpredictable and can change drastically within minutes at some places. One minute it’s a clear sky and the next minute it’s a thunderstorm. Temperatures can fall below zero degrees within minutes. Mountains are always under the threat of wide range of natural disasters, erosion, and lava flows.
Despite its unpredictable weather, mountains have great biodiversity and are home to thousands of species of animals and plants. Due to the sensitive living conditions on mountains, there is a large number of plants and animals that are endangered. Around 10% of the world’s human population too live on the mountains.
Types of mountains
Volcanic mountains: Volcanic mountains are formed when molten rocks from inside the Earth’s crust erupt and get piled up. Examples of volcanic mountains are, Mount Fuji in Japan and Mount St. Helens in Washington State.
Dome mountains: Dome mountains are formed when the magma merely pushes Earth’s crust up and hardens inside the crust, before erupting out of the surface. Rains and wind strike the domes, and sculpt valleys and summits. Popular examples are, the Black hills of South Dakota and Adriondack mountains of New York.
Plateau mountains: Formation of plateau mountains is similar to that of Dome mountains, except that, plateau mountains are formed due to tectonic activities, when tectonic plates push up the crust without faulting/folding. Plateau mountains are then shaped by erosion and weathering processes.
Fault-block mountains: These also occur due to tectonic activities. Fault-block mountains are formed when there is stress between tectonic plates. This leads to cracking of the surface of Earth, forcing the rocks up and down. Examples of fault-block mountains are, Sierra Nevada and Harz.
Hills have been homes to hundreds of people in rural as well as urban areas for hundreds and thousands of years. A lot of people build their homes on hills to avoid floods and defend themselves, for instance, the Ancient Rome.
Types of Hills
Drumlin: Drumlins are elongated hills (they look like an inverted spoon) formed by the movement of glacial ice on the underlying till. Drumlins occur in different sizes and shapes (parabolic, symmetric, etc.) and are typically 1 – 2 kms in length. They’re less than 50 meters high and are 300-600 meters wide and are mostly composed of glacial till, gravel and sand in varying proportions.
Drumlins form near glaciers/ice sheets and have most of glacially-formed features (scours, eskers, valleys).
Tor: Tors (castle koppies/kopjes) refer to the rock formation on top of hills or sometimes referred to the hill itself. These are free standing rocks, that rise on smooth surroundings. Tors are created by erosion/weathering of rocks like granites, dacites, dolerites, coarse sandstones, etc. and are mostly 5 meters high.
Puy: Puys are volcanic hills that are cone-shaped. Puys are also called as cinder cones and may or may not be associated with lava. They’re found in clusters or lines or sometimes isolated and scattered.
Pingo: Pingos are periglacial (or non-glacial) mounds of earth-covered ice, that are mostly found in Antarctica and Arctic & Subarctic regions. Pingos can reach up to a diameter of 600 meters and heights of up to 70 meters.
Plateaus have high flat surfaces which stretch for thousands of kilometers. Plateaus that are eroded by the flow of rivers are among the most uniform in terms of elevations, though their surfaces can be interrupted by canyons. Plateaus are formed by crustal shortening/volcanic activities/thermal expansion (of the lithosphere) and are found on most of the continents.
Erosion influences the shapes of plateaus in drastic ways. When the erosion is heavy, the plateaus are broken up into smaller raised landforms called as outliers, that are composed of old and dense rock formations. Outliers contain iron ore and coal.
Plateaus are broadly of two types:
Dissected and Volcanic plateaus.
Dissected Plateaus: Dissected plateaus are formed when tectonic plates collide slowly, resulting in an upward movement on the earth’s crust. A popular example is the Colorado Plateau (Western US) which has been rising 0.3 centimeters a year since 10 million years.
Volcanic Plateaus: Volcanic Plateaus are formed by lava that flows out of small volcanoes that slowly build up over time and form plateaus. For instance, the North Island Volcanic Plateau (Central part of North Island in New Zealand).
Intermontane plateaus: Intermontane plateaus are the highest plateaus in the world and are surrounded by mountains. The Tibetan plateau is the highest intermontane plateau.
Piedmont plateaus: Piedmont plateaus are plateaus that have mountains on one side and a sea/plain on the other. Popular examples are: Malwa Plateau, Patagonian plateau, etc.
Continental plateaus: These are vast plateaus that are surrounded on all sides by oceans/plains. Continental plateaus form away from the mountains. Example: Antarctic plateaus, Polar plateau, etc.
Grasslands: Grasslands are vast stretches of plain regions, with grass as the primary type of vegetation. The great plains, that are found across most of Central North America, are grasslands.
Prairies: Prairies are temperate grasslands, found in North America. Prairies can grow up to 1.5 meters high depending on the weather. Tall prairies are plowed under and aren’t usually farmland or pasture.
Steppes: Steppes are temperate grasslands of Eastern Europe and Asia. These areas do not receive enough rainfall to grow tall grass or trees.
Savannas: These are tropical grasslands, which exist in places with warm temperatures throughout the year. Savannas often have scattered trees and stretch across much of Central Africa and are also found in Australia and South America and some parts of the North America.
Not all the plains are grasslands. There are some plains that are forested (like the tabasco plain of Mexico). These have diverse types of vegetation, like trees and shrubs. Parts of the Sahara desert are plains. The Arctic areas also have plains and they’re called Tundra. Tundra are plains where the ground is frozen. Tundras, despite being cold, are home to a lot of plants, including moss and shrubs.
Types of plains
Flood plains: Flood plains, as the name suggests, are formed when sand, sediment and mud carried by floods pile up on land. Due to this reason, flood plains are extremely rich in nutrients and create a fertile land for farming. One of the most popular examples of flood plains, is the flood plain surrounding the Nile River of Africa, which has helped Egyptian civilization to thrive for centuries.
Alluvial plains: These plains form at the base of mountains; they’re formed when water carrying rocks and sediments flows downhill till it hits the flatland. The sediment is deposited on that plain (in the shape of a fan). One of the popular examples is the Huang He River in China, which has created an alluvial plain which stretches for kilometers. The Huang He River is also called as the Yellow River because of the yellow colored sediment it carries.
Coastal plains: When rivers carry sediment, and dump the sediment in the ocean, it builds up and eventually rises above the sea level, forming a coastal plain. These plains slope gently under water.
Abyssal plains: Abyssal plains are plains found at the bottom of all the oceans. These are approximately 5000-7000 meters below the sea level. Abyssal plains are considered as the flattest and smoothest surfaces on earth.
Apart from these major landforms, the earth has some minor landforms. They are:
Butte is a type of hill that usually stands isolated in a flat area. Buttes, like mountains, have steep sides and flat tops. Buttes are smaller than landforms such as plateaus, mesas and table. While mesas have wider tops, buttes have narrower tops.
One of the popular examples of Buttes is, the Mitten buttes in Arizona.
Buttes are formed by erosion and weathering.
Canyons are deep and narrow valleys in the crust of Earth’s surface. These are formed by flowing rivers that make deep cuts in the terrains. Canyons are also found on the ocean floors. One of the most popular canyons on Earth, is the Grand Canyon, which is cut by the Colorado River and is 277 miles long.
Types of canyons
Box canyon: Box canyons are formed when parts of wall collapse back on to the land. Box canyons’ heads are marked often by Cliffs on three sides of it.
Slot canyons: These are narrow pathways, sliced into eroding plateaus, by rushing river water. They’re very deep, though they are just few feet wide.
Submarine canyons: Submarine canyons are canyons formed underwater. These are similar to the ones on land but are cut by ocean currents. Most submarine canyons are extension of river canyons, that flow across the continental shelf.
Gorges: Small and steep-walled, V-shaped valleys, cut through by rivers that occur in upper courses of rivers, where the currents are strong and swift.
Valleys are formed by flowing rivers and movement of glaciers. These are elongated depressed areas on land which are washed out by the forces of ice and water. Valleys are usually U or V-shaped. Most valleys are cut through by streams/rivers. Valleys can occur on flat land or between hills and mountains. Valleys are usually drained rivers.
Types of valleys
Side valleys: Formed by tributaries of rivers.
Hollow valleys: Small-sized valleys that are nestled between hills or mountains.
Rifts: Giant valleys, when the crust of Earth is separated/split. Example: Great Rift Valley. Rift valleys are formed by tectonic activities.
Basins are shallow dip/depression on the surface of Earth. Basins occur in the shape of bowls. Basins have different shapes, like circular basins, oval-shaped basins, etc. While some basins are filled with water, others are dry. Basins are formed by erosions/earthquakes; while some take years to form, some are formed overnight.
Types of basins
River drainage basins: River drainage basins are basins which are drained by rivers and all their tributaries. They’re made up of watersheds. Every tributary or stream of rivers has its own watershed and these are part of the river basin. For example, the Mississippi river basin, is made up of six major watersheds, namely, Missouri, Upper Mississippi, Lower Mississippi, Askansas-Red-White rivers, Ohio and Tennessee.
The Amazon river basin is the world’s largest.
Structural basins: These are basins formed by Tectonic activity/weathering/erosion and are often found in dry areas. Structural basins look like a cluster of bowls stacked inside each other. Structural basins have internal drainage systems and don’t have sufficient water to drain into water bodies. Water that enters into these basins generally seeps inside the ground or evaporates and when a lot of water gets accumulated, it can become a salty late, like the dead sea.
Lake basin: Lake basin is a type of structural basin, which form in valleys that are blocked by rocks/debris left by landslides/glaciers/lava flow. These blockages act as dams and trap water to form a lake. Example: The Hunza Lake in Pakistan. Lake basins are also formed by movement of glaciers.
Sedimentary basin: Sedimentary basin, is also a type of structural basin, which sometimes form long troughs. They are filled with layers of organic material and rock (Sediment fill), which later become key sources of petroleum and other fuels.
Ocean basins: Ocean basins are some of the largest depressions on the surface of earth. The Continental shelves form the sides of these basins. The five major ocean basins on Earth are: the Atlantic basin, the Pacific basin, the Indian basin, the Arctic basin and the Southern basin. Ocean basins are formed and shaped by tectonic activities/spreading of seafloor/subduction and make up almost 70% of the land on Earth.
We hope the above helps you understand Landforms on Earth better.