Coastal Landform: Erosional & Depositional Features

Topic related to Geography BA Part I ( Honours unit III & Subsidiary unit II )

Dr Mohammad Zafar Iqbal Guest Faculty Department of Geography Kamla Rai College, Gopalganj Jai Prakash University Chapra Bihar India Introduction:

Coastal areas are an interface between the lithosphere and hydrosphere. Coastal zones are very sensitive zones. Coastal zones are not static but dynamic environments. They involve transformation of mass and energy through waves and currents. Shorelines are always subjected to both continental and oceanic processes. Waves, tides and currents are very powerful geomorphic agents. The erosional and depositional work of the sea waves can create many spectacular landscapes along the borders of the continents. Coastal landforms are interesting aspects in geomorphology. Sea waves, aided by winds, currents, tides and storms carry on the erosional and depositional processes. A Coastline represents the boundary between the continental land masses and the oceanic water masses. A Coastal zone is the transition zone between terrestrial habitat and the marine habitat. It is the interface between land and oceanic water. Coastal belts may be very wide or narrow. They also vary with reference to their slope, beach profile, rock types, climate and vegetation. The climate of a coast is basically controlled by the land and sea breezes. The climate is also controlled by the humidity of generated by the marine waters.

Coastal belts are further divided into three divisions as 1. Backshore region 2. Foreshore region and 3. Offshore region. 1. Backshore: The Backshore region represents the beach zone starting from the limit of storm wave, above high tide shoreline. This zone includes a wave cut terrace and a storm scarp. Beach is the sloping portion of the coast normally existing below the berms. This area is partly exposed by the backwash of waves (swash zone). 2. Foreshore: The Foreshore region is the region between high tide water zone and low tide water zone. It includes a Beach face and a beach terrace. The surf zone exists above beach terrace. At the end of the surf zone, the breaker zone starts. The foreshore may be a sandy foreshore, shingle foreshore, muddy foreshore or a rocky foreshore. Long shore currents occur in this zone, which run parallel to the coastline. 3. Offshore: The Offshore region represents the zone of oceanic shallow water zone extending fully inside the continental shelf. It begins after breaker zone. At the base, it includes the longshore troughs and longshore bars. Processes of coastal erosion: The combined effect of waves, currents and tides result in a variety of gradational processes acting in the coastal zone. Coastal erosion happens in the form of a) hydraulic action, b) corrosion (or) abrasion, c) attrition, d) corrosion (or) solution Hydraulic action is the impact of moving water on the coastal rocks. It is caused by the direct impact of waves on the coasts. Enormous pressures can build as water and air are compressed into the rock fractures. Abrasion (or) corrosion is a kind of erosion happening with the help of tools of erosion. In water suspension coarse sands, pebbles, cobbles and boulders are used by the waves to attack the coastal rocks. Attrition is a process in which mechanical tear and wear can break any rock mass into fragments. Mutual collision effected by backwash and rip currents are powerful tools of coastal erosion. Corrosion (or) Solution is the chemical alteration of rocks which are soluble and due to their contact with the seawater. Solution is locally important especially where soluble rock is exposed along the shore. EROSIONAL LANDFORMS

Landforms of coastal regions are classified into two major groups as erosional landforms and depositional landforms.

The notable erosional landforms of the coasts are: 1. Sea cliffs 2. Sea caves 3. Sea Arches 4. Sea stacks 5. Wave-cut notches 6. Wave-built terraces 7. Blow Holes or Spouting Horns 8. Cove Sea cliffs: The most widespread landforms of erosional coasts are sea cliffs. Wave erosion undercuts steep shorelines creating coastal cliffs. A sea cliff is a vertical precipice created by waves crashing directly on a steeply inclined slope. These very steep to vertical bedrock cliffs range from only a few metres high to hundreds of metres above sea level.

Sea caves: Sea caves form along lines of weakness in cohesive but well-jointed bedrock. Sea caves are prominent headlands where wave refraction attacks the shore. Sea Arches :When waves from opposite directions strike a narrow wall of rock, differential erosion of the rock leaves a bridge like structure called Sea arch.

Sea Stack: A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. When a portion of the sea arch collapses, the remaining column-like structure is called a stack, skarry or chimney rock. Wave-cut notches: Wave-cut platforms form when destructive waves hit against the cliff face, causing an undercut between the high and low water marks, mainly as a result of abrasion, corrosion and hydraulic action, creating a wave-cut notch. This notch then enlarges into a cave. Wave-built terraces: Wave-built terrace refers to a “gently sloping coastal surface entirely constructed at the seaward or lakeward edge of a Platform, Abrasion platformwave-cut platform by sediment brought by rivers or derived from the wave cutting and drifted along the shore or across the platform and deposited in the deeper water beyond” (Gary, McAfee, and Wolf, 1972). The term wave- built terrace originally referred to subaerial deposits of sand heaped along the shore edge of Lake Bonneville by exceptionally high storm waves (Gilbert, 1890). Blow Holes or Spouting Horns: The burst of water through a small hole on a sea cave due to the compression of air in the cave by strong waves. They make a peculiar noise. The Spouting Hole blowhole is a natural lava tube that releases a huge spout of water during large ocean swells, accompanied by a hiss and a roar. Cove: A cove is a small type of bay or coastal inlet. Coves usually have narrow, restricted entrances, are often circular or oval, and are often situated within a larger bay. Small, narrow, sheltered bays, inlets, creeks, or recesses in a coast are often considered coves. DEPOSITIONAL LANDFORMS

The notable depositional coastal landforms are: 1. Beaches 2. Spits and bars 3. Tombolo 4. Barrier islands 5. Mud Flats. Beaches: A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles. A beach is a deposit of loose sediment adjacent to a body of water. Spits and Bars: A sand spit is one of the most common coastal landforms. A sand spit is a linear accumulation of sediment that is attached to land at one end. Sand carried parallel to shore by longshore drift may eventually extend across a bay or between headlands especially where water is relatively calm. Spits are typically elongate, narrow features built to several dozen feet by wind and waves. Tombolo: A tombolo, from the Italian tombolo, derived from the Latin tumulus, meaning 'mound', and sometimes translated as ayre, is a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar. Once attached, the island is then known as a tied island. A tombolo is a sandy isthmus. Several islands tied together by bars which rise above the water level are called a tombolo cluster. Two or more tombolos may form an enclosure (called a lagoon) that can eventually fill with sediment. Barrier islands: Barrier islands are coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. Mudflats: Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A recent global analysis suggested they are as extensive globally as mangroves. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. References Bunnet, R. B. Physical Geography in Diagrams. New Delhi: Pearson Education, 2003. Hussain, M. Fundamental of Physical Geography. Jaipur: Rawat Publications, 2007. Singh, S. Physical Geography. Allahabad: Parayag Pustak Bhawan, 2003. Strahlar, A. and A. Strahlar. Physical Geography – Science and System of Human Environment. New York: John Wiley & Sons Inc., 1997. https://unsplash.com/photos/GKrux4c4Sbc Https://www.gettyimages.co.uk/photos/mud-flat https://en.wikipedia.org/wiki/Barrier_island https://www.britannica.com/science/tombolo https://en.wikipedia.org/wiki/Spit_(landform) https://commons.wikimedia.org/wiki/File:McWay_cog Thank You