Terrace (geology)

In geology a terrace is a step-like landform. It consists of a flat or gently sloping surface called the tread, usually bounded on one side by a steeper rising slope called the riser or scarp, and the tread together with the descending riser forms the terrace. Some terraces have a tread bounded by a descending riser on every side, and a narrow terrace is often called a bench. The sediments beneath the tread and riser are also commonly, though incorrectly, called terraces, which causes confusion. Terraces form in several ways. Fluvial terraces are remnants of a former floodplain, left when a river cuts down into its channel and abandons and laterally erodes the old floodplain, as a result of sea level change, uplift, climate, sediment load or discharge. Kame terraces form along the side of a glacial valley from meltwater streams flowing between the ice and the valley wall. Marine terraces record a former shoreline, cut by wave action or built from sediment or reef material, and are preserved when sea level falls or land rises. Lacustrine terraces mark the former shoreline of a lake.