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Rocky Coasts
Isabella Garramone
Oceanography Fall 2009
General Overview
• 75% of the world’s coasts are rocky.
• “As with most landforms rocky
shores reflect the structure and strength of the exposed lithologies, the physical and chemical processes acting on them, and the time they're allowed to do so. “
• Waves approach a shoreline from all sides in varying angles.
• The surf erodes softer rock faster than the surrounding rock.
• Rocky coasts have a narrow continental shelf that pitches sharply from land to sea.
Shaping of Rocky Coasts
• Physical Weathering: the erosion of land by waves, wind, or the movement of glaciers.
• Chemical Weathering: hydrolysis, oxidation, and salt weathering.
• Bioerosion: the erosion of land by algae or other organisms that either dissolve layers of rock or tunnel into it.
¾ Mainly on coasts made of carbonate.
Limestone bored by clams and sponges (bioerosion).
Geologic Features of Rocky Coasts
• Fjords: formed when glacial valleys fill with water when the sea lever rises.
• Pocket Beaches: protected embayments where wave action is subdued and sediment is not carried away.
• Sea Caves: carved out from bedrock by prolonged wave action.
• Sea Cliffs: a very steep slope separates flat land from the water.
• Sea Arches and Sea Stacks: isolated remnants of the mainland that will eventually be completely eroded away.
Pocket
Sea Cliff
•After caving in, a sea arch becomes a sea stack which will eventually become a sea stump.
Where are Rocky Coasts Found?
• Found where there is a history of erosion exceeding rates of sedimentation, or sediment is either low or not retained.
• Active Tectonic Environments
– volcanic islands: rapid uplift inhibits the development of sediment equilibrium (reef development is common)
– Example: parts of the coast of California
• Where Mountains and the Sea collide • Where glaciers played a large role in carving out the landscape; rapid glacial escape leaves little material behind to
make beaches.
– Examples: Maine & Alaska
Shipwreck Coast: Victoria, Australia
• Shipwreck Coast is made primarily of limestone.
• There are numerous sea stacks in the water & underwater rock formations that have sunken more than 200 ships.
Species that Live on Rocky Coasts
• Many species live in tide pools on top of the rocks, such as snails and macroinvertebrates.
• Algae, such as bladderwort, clings and grows off of the rocks.
• Smaller fish & organisms (such as juvenile lobsters) find refuge from predators in the underwater crevices the rocks provide.
• The animals living in the intertidal zones must be able to withstand being underwater and above water for prolonged periods.
• Barnacles attach themselves to the rocks as a base and use it as leverage to sweep the surrounding area for plankton.
Rocky Coasts + Global Climate Change
• As glaciers melt and sea level rises, rocky coastlines will become even more eroded than before.
• Many sea arches and sea stacks will tumble or some sea caves may enlarge or cave in.
• Increasingly turbulent storms as a results of warmer waters will erode the exposed rocks more rapidly.
• The waves produced by these larger storms will also erode the rocks at sea level more rapidly.
Works Cited
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Hanson, Lindsay S., . "Rocky Coasts." Geomorphology. Salem State College Department of Geological Sciences, Web. 23 Sep 2009. <http://w3.salemstate.edu/~lhanson/gls214/gls214_rocky.html>
"Oceans." Erosional and Depositional Features of Waves. Vancouver School Board, Web. 24 Sep 2009. <http://stloe.most.go.th/html/lo_index/LOcanada6/606/6_en.htm>.
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"Rocky Coasts." Geologic Features of Rocky Coasts. National Park Service, Web. 24 Sep 2009. <http://www.teachersdomain.org/ext/ess05_int_coastrock/05_R_GeoFeatures.ht
m>. Wilson, Mark A., . "Bioerosion." The College of Wooster Department of Geology, Web. 23 Sep 2009. <http://www3.wooster.edu/geology/Bioerosion/Bioerosion.html >.