A crack in geography is a narrow opening or fissure in a rock formation, usually caused by erosion or weathering. Cracks can be found in various landforms, such as mountains, cliffs and headlands. In coastal geography, cracks are important features that can lead to the formation of caves, arches, stacks and stumps.
Cracks are formed in the headland through the erosional processes of hydraulic action and abrasion. Hydraulic action is the force of the water hitting the rock, which creates pressure and weakens the rock. Abrasion is the scraping and grinding of rock fragments carried by the water, which wears away the rock surface. As the waves continue to grind away at the crack, it begins to open up to form a cave .
How do cracks lead to caves, arches, stacks and stumps?
The cave becomes larger and eventually breaks through the headland to form an arch . The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock) . The stack is undercut at the base until it collapses to form a stump . These features are erosional landforms that are commonly found on a headland.
What are some examples of cracks and their resulting landforms?
Some examples of cracks and their resulting landforms are:
The Green Bridge of Wales in Pembrokeshire is a fantastic example of an arch.
Stack Rocks, also in Pembrokeshire, are two stacks that were once part of an arch.
The Old Man of Hoy in Orkney is a famous stack that was formed from a crack in a cliff.
The Twelve Apostles in Australia are a group of stacks that were once part of a limestone cliff.
Durdle Door in Dorset is a natural limestone arch that was formed from a crack in a headland.
Caves, arches, stacks and stumps - Coastal landscapes - BBC
Coastal landforms - erosion and deposition - BBC Bitesize
Coastal Erosion National Geographic Society
What are the causes and consequences of coastal erosion?
Coastal erosion is the process by which local sea level rise, strong wave action, and coastal flooding wear down or carry away rocks, soils, and/or sands along the coast. All coastlines are affected by storms and other natural events that cause erosion; the combination of storm surge at high tide with additional effects from strong waves can be particularly damaging. Coastal erosion can also be influenced by human activities, such as construction, dredging, mining, and vegetation removal.
Coastal erosion can have significant impacts on the environment, economy, and society of coastal areas. Some of the consequences of coastal erosion are:
Loss of land and property: Coastal erosion can reduce the size and value of coastal lands and properties, and sometimes lead to their complete destruction. For example, along the Holderness Coast in England, more than 30 villages have been lost to the sea since Roman times due to coastal erosion.
Damage to infrastructure: Coastal erosion can damage or destroy roads, bridges, railways, pipelines, and other coastal infrastructure. This can disrupt transportation, communication, and energy supply, and increase the costs of maintenance and repair. For example, in 1990, a storm eroded a section of the railway line at Dawlish in Devon, cutting off rail links to southwest England for several weeks.
Threats to biodiversity: Coastal erosion can alter or destroy habitats for plants and animals along the coast, such as wetlands, dunes, beaches, and coral reefs. This can reduce biodiversity and affect ecosystem services such as water purification, nutrient cycling, and carbon sequestration. For example, in Louisiana, coastal erosion has contributed to the loss of about 25% of coastal wetlands since 1932, affecting the habitat of many species of fish, birds, and mammals.
Risks to human health and safety: Coastal erosion can increase the exposure and vulnerability of coastal communities to hazards such as storms, floods, landslides, and tsunamis. This can result in injuries, deaths, displacement, and psychological stress for coastal residents. For example, in 2004, a tsunami triggered by an earthquake off the coast of Sumatra eroded many beaches and coastal settlements in Indonesia, Sri Lanka, India, Thailand, and other countries, killing more than 200000 people.