Coastal Geology and Processes
by Owen Borville
January 30, 2021
Learning, Geology, Science
Tides have a large influence on coastal areas and are caused by the gravitational pull of the Moon and the Sun. The gravitational pull of the Moon on Earth is greater than the gravitational pull of the Sun. Tides cause the ocean on the side of the Earth facing the Moon to bulge out slightly, which raises the sea level. Another tidal bulge occurs on the other side of the Earth as water lags behind due to weaker gravitational attraction. These bulges create a high tide.
Flood tide is the tide associated with rising sea level and coastal areas becoming submerged with water. Ebb tide is the outgoing tide when sea level decreases after a flood tide.
Spring tide occurs twice monthly when the Sun, Moon, and Earth are in alignment (at the time of the new or full Moon), and the solar (Sun) tide has an additive gravitational effect on the lunar (Moon) tide, creating very large high tides. Neap tide occurs twice monthly when the Sun and Moon are at right angles to each other and the solar tide partially cancels out the lunar tide, which produces moderate tides.
Coastal wave morphology includes the wave crest, which is the highest point on a wave. The wave trough is the low point of a wave between crests. The wavelength is the distance between successive points of equal amplitude and phase on a wave (for example, crest to crest or trough to trough). The wave height is the vertical distance between the crest and the preceding trough of a wave. The wave period is the amount of time for two successive wave crests to pass a stationary point.
Wave base is the downward limit of wave motion in the water and is directly related to how far apart the waves are at the surface. The depth of the wave base is equal to about half the wavelength. The fetch is the surface area in which ocean waves are generated by the wind. Fetch also refers to the length of the fetch area, measured in the direction of the wind.
Swells are wind-generated ocean waves that have traveled out of their source region, usually over a considerable distance. Swell waves exhibit a more regular and longer period or wavelength with flatter crests than locally generated wind waves.
Breaking waves occur where waves enter shallow water areas near the shore. Friction from the seafloor slows the wave near the wave base while the water at the wave crest piles up until it can no longer be supported and the wave breaks.
Wave refraction occurs when ocean waves bend as a result of decreasing water depth and become more parallel with the shoreline (waves travel slower in shallower water and faster in deeper water). Wave diffraction occurs when a travelling wave contacts with an obstacle and causes the waves to bend around the obstacle or when a wave spreads out past small openings.
A rip current is a relatively small-scale surf-zone current moving away from the beach. Rip currents form as waves disperse along the beach which causes water to become trapped between the beach and a sandbar or other underwater feature. The water converges into a narrow, river-like channel moving away from the shore at high speed. Rip currents most typically form at low spots or breaks in sandbars and also near structures such as groins, jetties, and piers.
A beach is land adjacent to a body of water such as an ocean, sea, or lake. A beach can consist of sand, gravel, shingle, pebbles, cobbles, shell fragments, and coralline algae fragments. The backshore is the section of the beach which is submerged only during the highest tides and severest storms. The berm is the sandy, nearly horizontal step-like feature on the backshore of a beach. The foreshore is the part of the shore lying between the berm crest and the ordinary low water mark, which is ordinarily traversed by the upbrush and backwash of the waves as the tides rise and fall. The swash zone is the zone of wave action on the beach.
Longshore current causes water waves to hit the coastline at an angle and as a result causes water to move parallel to the coastline. The waves enter the coastline at an angle, however, the waves retreat perpendicular to the coastline.
Longshore drift (littoral drift) is the moving of sediment parallel to the coastline and is caused by longshore current. Longshore current causes waves to hit the coastline at an angle and retreat perpendicular to the coastline. The sediment follows the pattern of the current so that the sediment is deposited further down current from the original position.
A groin is a man-made wall which is built on a beach perpendicular to the coastline. A groin points outward into the water and allows the beach to collect sand from longshore currents to protect the beach and extend the beach further outward. A jetty is defined as an engineering structure that projects perpendicular to the coastline and is typically composed of large blocks of rock designed to reduce the flow of sand into a coastal navigation channel, such as a tidal inlet. Seawalls and breakwaters are also built to protect the shoreline from erosion and build up the sand at the beach.
A spit is a small point of land or a narrow shoal projecting into a body of water from the shore. A spit is affected by longshore sediment erosion and accretion. A baymouth bar is a spit that has grown to completely close off the bay from the sea. A recurved spit is a coastal land projection that has a curved shape and is caused by longshore current depositing and moving sediment. A tombolo is a bar or spit of sand that connects or ties an island to the mainland or to another island.
Barrier islands are long, narrow islands located parallel to the mainland and separated by estuaries, bays, and lagoons on a gently sloping continental shelf. These islands provide protection to the mainland from the brunt of ocean waves and are considered dynamic environments, as they are constantly being shaped and reshaped, eroded, and accreted. Their formation depends on sand supply, wave energy, and tidal fluctuations. These islands typically occur in chains which are separated from each other by tidal inlets.
Sea cliffs occur on coastlines and were carved and directly affected by wave erosion. A marine terrace is a flat coastal platform and begins as a wave-cut platform. Eustatic sea level changes, sea cliff erosion, and tectonic uplift work together to generate marine terraces. Sea arches commonly form on rocky cliff coastlines where wave erosion or dissolution has carved into the rocky cliff to form an arch. Sea caves form by wave erosion or dissolution similar to sea arches, as rock is removed from one side of the cliff and does not reach the other side. Sea caves can become sea arches after continued erosion or dissolution. Sea stacks are the seaward side remains of sea arches which have collapsed.
Submergent coastlines occur as sea level rises with respect to the land or by land subsidence. An estuary is a semi-enclosed body of water which has a free connection to the open sea and within which seawater is measurably diluted by fresh water derived from land drainage. Estuaries form as a result of submergent coastlines. Emergent coastlines are stretches along the coast that have been exposed by the sea due to a relative fall in sea level. Marine terraces can result from emergent coastlines.
by Owen Borville
January 30, 2021
Learning, Geology, Science
Tides have a large influence on coastal areas and are caused by the gravitational pull of the Moon and the Sun. The gravitational pull of the Moon on Earth is greater than the gravitational pull of the Sun. Tides cause the ocean on the side of the Earth facing the Moon to bulge out slightly, which raises the sea level. Another tidal bulge occurs on the other side of the Earth as water lags behind due to weaker gravitational attraction. These bulges create a high tide.
Flood tide is the tide associated with rising sea level and coastal areas becoming submerged with water. Ebb tide is the outgoing tide when sea level decreases after a flood tide.
Spring tide occurs twice monthly when the Sun, Moon, and Earth are in alignment (at the time of the new or full Moon), and the solar (Sun) tide has an additive gravitational effect on the lunar (Moon) tide, creating very large high tides. Neap tide occurs twice monthly when the Sun and Moon are at right angles to each other and the solar tide partially cancels out the lunar tide, which produces moderate tides.
Coastal wave morphology includes the wave crest, which is the highest point on a wave. The wave trough is the low point of a wave between crests. The wavelength is the distance between successive points of equal amplitude and phase on a wave (for example, crest to crest or trough to trough). The wave height is the vertical distance between the crest and the preceding trough of a wave. The wave period is the amount of time for two successive wave crests to pass a stationary point.
Wave base is the downward limit of wave motion in the water and is directly related to how far apart the waves are at the surface. The depth of the wave base is equal to about half the wavelength. The fetch is the surface area in which ocean waves are generated by the wind. Fetch also refers to the length of the fetch area, measured in the direction of the wind.
Swells are wind-generated ocean waves that have traveled out of their source region, usually over a considerable distance. Swell waves exhibit a more regular and longer period or wavelength with flatter crests than locally generated wind waves.
Breaking waves occur where waves enter shallow water areas near the shore. Friction from the seafloor slows the wave near the wave base while the water at the wave crest piles up until it can no longer be supported and the wave breaks.
Wave refraction occurs when ocean waves bend as a result of decreasing water depth and become more parallel with the shoreline (waves travel slower in shallower water and faster in deeper water). Wave diffraction occurs when a travelling wave contacts with an obstacle and causes the waves to bend around the obstacle or when a wave spreads out past small openings.
A rip current is a relatively small-scale surf-zone current moving away from the beach. Rip currents form as waves disperse along the beach which causes water to become trapped between the beach and a sandbar or other underwater feature. The water converges into a narrow, river-like channel moving away from the shore at high speed. Rip currents most typically form at low spots or breaks in sandbars and also near structures such as groins, jetties, and piers.
A beach is land adjacent to a body of water such as an ocean, sea, or lake. A beach can consist of sand, gravel, shingle, pebbles, cobbles, shell fragments, and coralline algae fragments. The backshore is the section of the beach which is submerged only during the highest tides and severest storms. The berm is the sandy, nearly horizontal step-like feature on the backshore of a beach. The foreshore is the part of the shore lying between the berm crest and the ordinary low water mark, which is ordinarily traversed by the upbrush and backwash of the waves as the tides rise and fall. The swash zone is the zone of wave action on the beach.
Longshore current causes water waves to hit the coastline at an angle and as a result causes water to move parallel to the coastline. The waves enter the coastline at an angle, however, the waves retreat perpendicular to the coastline.
Longshore drift (littoral drift) is the moving of sediment parallel to the coastline and is caused by longshore current. Longshore current causes waves to hit the coastline at an angle and retreat perpendicular to the coastline. The sediment follows the pattern of the current so that the sediment is deposited further down current from the original position.
A groin is a man-made wall which is built on a beach perpendicular to the coastline. A groin points outward into the water and allows the beach to collect sand from longshore currents to protect the beach and extend the beach further outward. A jetty is defined as an engineering structure that projects perpendicular to the coastline and is typically composed of large blocks of rock designed to reduce the flow of sand into a coastal navigation channel, such as a tidal inlet. Seawalls and breakwaters are also built to protect the shoreline from erosion and build up the sand at the beach.
A spit is a small point of land or a narrow shoal projecting into a body of water from the shore. A spit is affected by longshore sediment erosion and accretion. A baymouth bar is a spit that has grown to completely close off the bay from the sea. A recurved spit is a coastal land projection that has a curved shape and is caused by longshore current depositing and moving sediment. A tombolo is a bar or spit of sand that connects or ties an island to the mainland or to another island.
Barrier islands are long, narrow islands located parallel to the mainland and separated by estuaries, bays, and lagoons on a gently sloping continental shelf. These islands provide protection to the mainland from the brunt of ocean waves and are considered dynamic environments, as they are constantly being shaped and reshaped, eroded, and accreted. Their formation depends on sand supply, wave energy, and tidal fluctuations. These islands typically occur in chains which are separated from each other by tidal inlets.
Sea cliffs occur on coastlines and were carved and directly affected by wave erosion. A marine terrace is a flat coastal platform and begins as a wave-cut platform. Eustatic sea level changes, sea cliff erosion, and tectonic uplift work together to generate marine terraces. Sea arches commonly form on rocky cliff coastlines where wave erosion or dissolution has carved into the rocky cliff to form an arch. Sea caves form by wave erosion or dissolution similar to sea arches, as rock is removed from one side of the cliff and does not reach the other side. Sea caves can become sea arches after continued erosion or dissolution. Sea stacks are the seaward side remains of sea arches which have collapsed.
Submergent coastlines occur as sea level rises with respect to the land or by land subsidence. An estuary is a semi-enclosed body of water which has a free connection to the open sea and within which seawater is measurably diluted by fresh water derived from land drainage. Estuaries form as a result of submergent coastlines. Emergent coastlines are stretches along the coast that have been exposed by the sea due to a relative fall in sea level. Marine terraces can result from emergent coastlines.
