Geomorphology is the branch of science that examines the outer surface of the Earth, the shapes on it (mountains, valleys, plains, etc.) and how these shapes are formed and how they change. In short, it is the science of the shapes of the earth. The earth is a dynamic place that is constantly changing and geomorphology helps us understand this change. This science investigates the natural processes that create landforms (forces such as water, ice, wind, volcanism, tectonic movements) and the effects of these processes over time. Geomorphology is important for understanding not only the current state of the surface, but also its past and how it may change in the future. Understanding landforms is vital for managing natural resources, predicting natural hazards and environmental planning.
Geomorphologists work to explain why a mountain has a particular shape, why a river meanders or how the dunes of a desert are formed. This work involves observing, measuring and modeling physical processes. Landforms can be the result of millions of years of slow changes or sudden and violent events (earthquakes, volcanic eruptions, floods).
Basic Natural Processes and Mechanisms that Shape the Earth
There are many natural processes that create and change landforms. These processes are often related to the energy sources acting on the Earth’s surface. Solar energy drives winds and the water cycle, while the Earth’s internal heat triggers volcanism and tectonic movements. Gravity is the main driver of mass movements (slope slides).
These processes are usually described in three main stages:
- Erosion: The breaking up and loosening of rocks and soil.
- Transportation: The movement of eroded material from one place to another (by water, wind, ice, gravity).
- Deposition: Leaving the transported material in places where energy is reduced and new landforms are formed.
Here are the main categories of geomorphological processes and how they shape the earth:
Fluvial Processes
Fluvial processes study the ways in which rivers and streams shape the earth’s surface. Water is one of the most powerful geomorphologic agents. Streams work by excavating their beds, eroding their banks, dragging the material they carry and finally depositing it.
- Erosion: The excavation of the bed and banks of a river by the force of water, by the grinding of the bed by the gravel it carries, or by chemical dissolution.
- Transport: It is the dragging of the material (mud, sand, gravel, rock fragments) eroded by the river with the force of the flow of water. The material can be transported in suspension (suspended), by rolling, splashing or dissolved.
- Accumulation: When the flow rate and carrying capacity of the river decreases (in cases such as decreasing the slope, spreading over a large area, reaching the sea / lake), it leaves the material it carries.
Landforms Formed by Fluvial Processes and Examples:
- Valleys: Formed when rivers erode their beds. Young valleys are usually V-shaped, deep and narrow (e.g. river valleys in high mountains). As the river matures, the valley widens and the bottom may flatten.
- Canyons: They are deep valleys with steep slopes. They are usually formed by the rapid erosion of high plateaus by rivers.
Example: Grand Canyon in the USA. It is the result of millions of years of deep erosion of plateau layers by the Colorado River. This is a well-known example of the immense power of fluvial erosion. [1] - Meanders: They are large meanders drawn by rivers in plains where the slope decreases. The meanders grow over time by erosion in the outer curves of the river bed and accumulation in the inner curves.
Example: The middle parts of the Büyük Menderes River in Turkey or the Mississippi River in the USA have a meandering structure. - Flood Plains: They are flat and fertile areas formed by the accumulation of fine materials carried by the river from its bed during flood times.
- Deltas: They are triangular or bird’s foot shaped plains formed by the accumulation of alluvial (deposit) material carried by a river where it flows into the sea or lake. The speed of the river drops suddenly here and the carrying power is lost.
Example: Nile Delta in Egypt, Çukurova Delta in Turkey (Seyhan and Ceyhan Rivers). These are fertile agricultural areas formed by the accumulation of material carried by rivers to the sea. - Terraces: In river valleys, they are formed when the old valley floor is left in the form of steps on the sides as a result of the re-digging of the river bed or the rise of the bed.
Glacial Processes
Glacial processes are the shaping of the Earth’s surface by the movement and interaction of ice masses (glaciers). Because they are large and heavy, glaciers can erode the rocks beneath and beside them, transport large amounts of material and deposit it in different places.
- Erosion: Glaciers erode the rocks below and next to them in two main ways:
- Plucking: The glacier seeps into cracks in the ground and freezes. As it moves, it rips off pieces of rock that stick to the ice.
- Abrasion: The glacier abrades and scratches the surface like sandpaper by rubbing the rock and sand particles it takes in against the ground beneath it.
- Transportation: The glacier can carry the material it breaks off or falls on inside the ice mass or on its surface. Glaciers work like giant trucks.
- Accumulation: When the glacier melts, it leaves all the material it has carried (called glacial deposits or moraines) in place.
Landforms Formed by Glacial Processes and Examples:
- U-shaped valleys: In contrast to the V-shaped valleys of rivers, glaciers form U-shaped valleys with wide floors and steep slopes. The glacier fills the entire valley, eroding both the bottom and the sides.
Example: Yosemite Valley in the USA was once a glacial valley. - Fjords: U-shaped coastal valleys eroded by glaciers to below sea level and filled by seawater after the glacier retreats. They are usually steep and high-sided.
Example: Norwegian Fjords or Milford Sound in New Zealand. They are impressive coastal examples of glacial erosion. - Moraines: Piles of poorly-sorted material (i.e. containing different sizes of rock and mud) carried and deposited by glaciers. They can be in front of the glacier (terminal moraine), beside it (lateral moraine) or underneath it (ground moraine).
- Cirques: These are amphitheater-shaped depressions formed by glacial erosion in the mountains where the glacier formed. They usually have steep slopes and may contain small lakes (cirque lake).
- Roche Moutonnée: These are rock masses parallel to the direction of the glacier’s movement, with one side rasped (smoother) and the other side broken off by plucking (rougher). They show the direction of movement of the glacier.
Wind (Aeolian) Processes
Wind processes are the effects of wind eroding, transporting and depositing the earth’s surface. These processes are particularly effective in arid and semi-arid regions (deserts) where vegetation is sparse, but can also occur in coastal regions or agricultural areas.
- Erosion: Wind erodes in two ways:
- Deflation: Wind directly blows away loose, fine-grained material (sand, silt, dust). This can create depressions in the ground.
- Corrosion: When grains of sand and dust carried by the wind strike rocks or other surfaces, sanding or roughening the surface. This effect is usually more intense near ground level.
- Transportation: Wind carries material in different ways depending on its size and the speed of the wind: drag, saltation and suspension. Fine dust can be carried for many kilometers.
- Accumulation: When the speed of the wind decreases, it deposits the material it is carrying. Sands are usually deposited as dunes, while finer silt and dust can be deposited in thick layers called loess.
Landforms Formed by Wind Processes and Examples:
- Sand Dunes: Formed when sand carried by the wind is deposited in the form of dunes or ridges where the wind speed decreases. Dunes have different shapes (crescent-shaped barchans, longitudinal seifs, etc.) and their shape depends on the direction of the wind and the amount of sand.
Example: Ergs (vast seas of dunes) in the Sahara Desert or the Karakum Desert in Central Asia. These are the largest-scale examples of the depositional power of wind. - Yardangs: Long, streamlined ridges parallel to the wind direction, formed by wind erosion (corrosion), especially in deserts. The soft material between them has been eroded by the wind.
- Loesses: Formed when very fine, clay and silt-sized material carried by the wind from near glaciers or dry river beds is transported thousands of kilometers away and deposited in thick layers. Loess soils are usually very fertile.
Example: The Loess Plateau in China is a huge and fertile area of wind-blown loess deposits.
Coastal Processes
Coastal processes are the earth-shaping effects of waves, currents and tides on the shores of the sea or large lakes. Coasts are dynamic and rapidly changing environments as they are the interaction area of land, sea and atmosphere.
- Erosion: The breaking up and transportation of the coast by waves and currents. This includes hydraulic pressure (when waves hit and compress rock), abrasion (when material carried by waves hits the shore) and chemical dissolution.
- Transport: The movement of sand and gravel along the shore by waves and currents along the coast (longshore current).
- Deposition: The accumulation of material carried by waves or currents in bays where the energy of the waves or currents decreases or at points where the currents change direction, forming beaches or coastal features.
Landforms Formed by Coastal Processes and Examples:
Beaches: Areas formed by the accumulation of sand, gravel or shells carried by waves and currents. The shape and material of beaches depend on wave energy and the source of the material.
- Cliffs: High and steep cliffs formed as a result of the steepening of the coasts by wave erosion. Waves may erode the bottom of the cliffs to form a sea cave, and as this cave grows, the ceiling may collapse and the cliff retreats.
Example: The White Cliffs of Dover in England or the cliffs along the Black Sea coast in Turkey. These show the powerful effect of wave erosion. - Coastal Spits and Tombolos: The accumulation of sand carried by currents along the coast in the form of narrow sand spits (coastal spits) or dune ridges (tombolo) that connect an island to the mainland.
- Lagoons: Shallow bodies of water separated from the sea or connected by a narrow passage, formed when the front of a bay is blocked by a coastal spit or dune ridge.
Tectonic Processes
Tectonic processes are related to the movement of the large plates that make up the Earth’s solid outer crust (lithosphere). These processes trigger large-scale landforms and events such as the uplift of mountain ranges, the collapse of valleys, the formation of fault lines and earthquakes. Tectonic processes usually work very slowly (a few centimeters per year), but with sudden movements (earthquakes) they can cause instant and large changes. Tectonism is a structural control mechanism that acts on other geomorphological processes.
- Plate Movements: When plates move closer together (collision), farther apart (separation) or slide side to side.
- Faulting: The displacement and fracturing of rocks and their movement to different levels. This creates fault lines and fault steps.
- Folding: The bending of rocks under compressive forces to form anticlinal (dome-shaped) and synclinal (bowl-shaped) structures.
- Uplift/Lowering: The slow rise or fall of large areas.
Landforms Formed by Tectonic Processes and Examples:
- Fold Mountains: They are formed when the layers in the earth’s crust fold and rise as a result of the collision of the plates.
Example: Himalayas, Alps, Andes Mountains are huge fold mountains formed by the collision of tectonic plates. [2] - Fault Mountains and Rift Valleys: Fault mountains (horst) and rift valleys (graben) are formed when the earth’s crust breaks along fault lines and rises in blocks.
Example: The East African Rift Valley System is a huge area of tectonic subsidence formed when the African plate began to split in two. - Volcanoes: Places where magma rises to the surface, usually at plate boundaries (although volcanism is a separate category, it is often closely related to tectonic activity).
Volcanic Processes
Volcanic processes encompass all the events related to the rise of magma (molten rock) through the Earth’s interior, reaching the surface and solidifying. These processes can create new landforms and change existing ones.
- Eruption: When magma rises to the surface in the form of lava, ash, gas and rock fragments.
- Lava Flows: Lava flows along the slope and cools and solidifies.
- Ash and Tephra Accumulation: Accumulation of material blown into the air by explosive eruptions and falling to the ground.
Landforms Formed by Volcanic Processes and Examples:
- Volcano Mountains: Formed by piling up lava, ash and other material accumulated as a result of eruptions. There are different types (shield volcanoes – Hawaii, stratovolcanoes – Fuji, Vesuvius).
Example: Mount Fuji in Japan (a stratovolcano) or Kilauea Volcano in Hawaii in the USA (a shield volcano). These are examples of distinctive volcanic landforms formed by different types of volcanic eruptions. - Calderas: Huge depressions formed when the top of a large volcano collapses inward as a result of an eruption or the emptying of the magma chamber beneath it. Lakes can form in them.
Example: Crater Lake (Oregon) in the USA is a lake formed in a caldera. - Lava Plateaus: Large, flat areas formed when very fluid lava spreads over large areas and accumulates in thick layers.
Example: The Columbia River Plateau in the USA.
Karstic Processes
Karst processes are related to water chemically dissolving soluble rocks such as limestone (calcium carbonate), gypsum or rock salt. These processes create unique landforms underground and on the surface.
Dissolution: When rainwater takes in carbon dioxide (CO2) from the atmosphere or soil and becomes slightly acidic, and when this acidic water comes into contact with soluble rocks (especially limestone) it dissolves them.
Landforms Formed by Karstic Processes and Examples:
- Caves: They are formed when underground water dissolves rocks and creates cavities. Stalactites (hanging from the ceiling) and stalagmites (rising from the ground) can be formed by the accumulation of minerals carried by water inside the caves.
Example: Postojna Cave in Slovenia or Damlatas Cave in Turkey. These are complex underground systems created by the dissolution power of groundwater. - Sinkholes: Funnel- or bowl-shaped depressions where surface water flows underground or where the ceiling of a cave collapses.
Example: Cenotes on the Yucatan Peninsula in Mexico are water-filled sinkholes formed by the collapse of underground cave systems. - Lapies: Indented and protruding surfaces consisting of small hollows, grooves and ridges formed by surface dissolution in karst areas.
- Polje: In karstic areas, these are large closed depressions with steep sides and flat bottoms formed by the merger of more than one sinkhole or by tectonic movements.
Biogenic Processes
Biogenic processes are geomorphological impacts related to the physical or chemical influence of living organisms (plants, animals, microorganisms) on the earth’s surface.
- Physical Impacts: Plant roots breaking down rocks, animals dig burrows and move the soil, microorganisms breaking down rocks.
- Chemical Impacts: Chemicals secreted by organisms such as lichens dissolve rocks, corals form carbonate skeletons and build reefs.
Landforms Formed by Biogenic Processes and Examples:
- Coral Reefs: Huge underwater structures formed by billions of tiny coral polyps building carbonate skeletons. They are one of the largest structures created by living organisms on Earth.
Example: The Great Barrier Reef in Australia is the largest and most famous structure created by biogenic processes. - Peatlands: Layers of organic soil formed by the accumulation of plant material in swampy areas without complete decomposition. This accumulation can form distinctive topographic shapes on the surface.”
- Micro-topography formed by termite nests: Especially in tropical regions, large nests built by termites can form prominent mounds on the ground surface.
Interaction of Geomorphological Processes and Time Scales
These geomorphological processes do not usually work independently of each other. Most landforms are the result of the interaction of multiple processes over long periods of time. For example, a mountain range is formed by tectonic uplift, which is then broken up by rivers through valleys, its higher parts eroded by glaciers and its coasts shaped by waves. Global factors such as climate change can affect all these processes.
Geomorphological changes occur on different time scales:
- Sudden Events: Events such as earthquakes, volcanic eruptions, landslides, floods can dramatically change the earth’s surface within hours or days.
- Medium Term Processes: Processes such as shifting riverbeds, advancing dunes, retreating coasts can take years or decades.
- Long-Term Processes: Processes such as mountain building, the movement of continents, the formation of large valley systems or deltas take thousands or millions of years.
Geomorphological Hazards
Geomorphological hazards are conditions of natural geomorphological processes that adversely affect human life, property or the environment. These hazards are often associated with sudden or rapidly evolving processes and constitute an applied area of geomorphology.
- Landslides and Slope Slides: The downward movement of soil, rock or debris on slopes under the influence of gravity. It can be triggered by excessive rainfall, earthquakes or human activities (such as road construction) that disturb the slope balance.
- Ground Subsidence: It is the downward movement of the ground surface as a result of the collapse of underground cavities (caves – karstic subsidence, mine galleries) or excessive withdrawal of fluids such as groundwater/oil.
Example: Cities such as Mexico City or Venice suffer from ground subsidence. The causes include groundwater extraction and the natural structure of the ground. [3] - Soil Erosion: The transportation of the top layer of soil by wind or water. Although it is a natural process, it can be accelerated by improper agricultural practices (logging, overgrazing) and can cause great damage to agricultural land.
- Floods: The flooding of surrounding areas by water in excess of the carrying capacity of river beds. They can be caused by heavy rainfall, snowmelt or dam failures.
- Coastal Erosion: This is when waves and currents shift the shoreline landward. Sea level rise and human structures on the coast can accelerate this process.
- Volcanic Hazards: Hazards associated with volcanic eruptions, such as lava flows, pyroclastic flows (hot gas and rock avalanches), ash showers and volcanic mud flows (lahars).
- Earthquakes and Tsunamis: Sudden ground shaking caused by tectonic plate movements (earthquakes) and giant waves triggered by earthquakes on the seafloor (tsunamis).
Human” Impact on Geomorphology
By building dams (altering river regime and deposition), cutting down forests (increasing erosion), building cities (increasing runoff and impervious surfaces), mining (altering surface and subsurface structure), agriculture (affecting soil erosion) and changing the climate (melting glaciers, sea level rise, extreme weather events), human beings significantly influence geomorphological processes and have become a geomorphological agent in their own right. This is a separate field of study called Anthropogenic Geomorphology.
How Geomorphology is studied?
Geomorphologists use various methods to understand landforms:
- Field Studies: Direct on-site observation, taking measurements, collecting rock and soil samples.
- Mapping and Remote Sensing: Using technologies such as topographic maps, aerial photographs, satellite imagery, Lidar, etc. to study large areas and track changes.
- Laboratory Analyses: Determining the age, chemical composition and physical properties of field samples.
- Modeling: Using computer programs to simulate and predict the effects of geomorphological processes over time.
Conclusion
Geomorphology is a fundamental science for understanding why the world around us looks the way it does. The Earth is a dynamic system shaped by powerful natural processes that are constantly at work. Streams, glaciers, wind, waves, volcanism and tectonic movements are constantly reshaping the surface of our planet, each in its own unique way, carving valleys, raising mountains, changing coasts and transporting debris. Understanding these processes is critical for coping with natural hazards, predicting environmental changes and managing our place on Earth in a more informed way. By reading the traces of the past, geomorphology allows us to understand the present and predict the future.