A marine terrace is a flat portion of land on a coastline that overlooks the water and somewhat resembles a staircase. Marine terraces can have very high walls, and some are large enough to build towns or colonies upon. Marine terraces are formed by a specific geological process that incorporates erosion and by a buildup of coral. They are also known as raised beaches or perched coastlines.
Geological Process
Marine terraces in cooler climates are formed through a combination of erosion, abrasion and sea level change. Waves carry sediment that scrapes along a sea wall, breaking off small pieces of it and carrying it away. The sea wall is worn down and flattened over time. A marine terrace results when the water recedes during sea-level change, revealing the flat portion that was created by the erosion and abrasion. Tectonic uplift (when tectonic plates push land up) sometimes contributes to moving portions of marine terraces even farther above sea level. Tectonic uplift sat different times during many thousands of years form the stair-step terraces.
Biological Marine Terraces
In warm climates, marine terraces are formed by coral. Corals will begin growing at the top of the low-tide line and then spread out laterally. The continued spreading of the coral eventually creates a coral flat, mimicking the appearance of a marine terrace formed through geological means.
Sediments
The sediment found on marine terraces is usually very thin. It is composed of sediment typically found in the ocean, since the platforms were once underwater. Typical marine terrace sediment includes marine fossils, shells, and sand. The oceanic sediment is further proof that the terraces are formed by the fluctuations in sea level combined with erosion and abrasion.
Age
Marine terraces take many thousands of years to form. In California, one of the highest terraces is 600 feet high yet has taken 500,000 years to form. The strength of currents will affect the rate at which the terraces form, as stronger waves lead to stronger erosion and abrasion. Biological terraces take significantly less time to form, as their growth depends on the speed at which a particular population of coral can spread.
Tags: erosion abrasion, marine terrace, terraces formed, years form, flat portion, formed through
