6.9. HIGH ROCKY COASTS

Along the high rocky coasts, the rivers appear to have been drowned with highly irregular coastline. The coastline appears highly indented with extension of water into the land where glacial valleys (fjords) are present. The hill sides drop off sharply into the water. Shores do not show any depositional landforms initially. Erosion features dominate.

High rocky coasts are defined by their steep and irregular contours. The rivers found in these areas seem submerged, creating a rugged appearance known as an indented coastline. This occurs because, in the past, glaciers have carved out deep valleys (fjords) that extend inland, leading to sharp drops where land meets the sea. At these coasts, you won’t see many areas where sediments are built up to form new land (depositional landforms) due to the overwhelming force of erosion.

Think of a giant sandwich where each layer is distinct and layered at an angle. Now imagine the top of the sandwich is missing, exposing the fillings underneath. This is similar to how high rocky coasts look; steep cliffs drop into the water below, resembling the sharp drop of an exposed sandwich filling.

Along high rocky coasts, waves break with great force against the land shaping the hill sides into cliffs. With constant pounding by waves, the cliffs recede leaving a wave-cut platform in front of the sea cliff. Waves gradually minimize the irregularities along the shore.

The power of waves crashing against cliffs shapes high rocky coasts significantly. Over time, as waves continuously hit the steep cliffs, they erode the base of the cliffs, causing them to retreat. This process creates a flat area at the water's edge called a wave-cut platform. As the waves continue to wash against the land, they smooth out the edges, making them less jagged.

Imagine repeatedly pushing a rock with a basketball. Each push wears down the bottom of the rock, making it flatter until it resembles a table surface. This is like how waves constantly attack cliffs, smoothing them out over time until they form a flat area in front.

The materials which fall off, and removed from the sea cliffs, gradually break into smaller fragments and roll to roundness, will get deposited in the offshore. After a considerable period of cliff development and retreat when coastline turns somewhat smooth, with the addition of some more material to this deposit in the offshore, a wave-built terrace would develop in front of wave-cut terrace.

As cliff erosion continues, bits of rock and sediment break away from the cliffs. These fragments are worn down by waves and currents and eventually settle in deeper water offshore, creating new landforms. Over time, as the cliffs continue to erode and the offshore areas build up with sediment, they can form a wave-built terrace, which is like a sloped shelf extending into the sea.

Think of how a sculptor carves a statue from a large stone block. As the sculptor works and chips away at the stone, small pieces fall away. Eventually, those small pieces might pile up at the base, creating a platform that builds up over time. Similarly, the erosion of cliffs allows materials to accumulate offshore, forming terraces.

As the erosion along the coast takes place, a good supply material becomes available to longshore currents and waves to deposit them as beaches along the shore and as bars (long ridges of sand and/or shingle parallel to the coast) in the nearshore zone. Bars are submerged features and when bars show up above water, they are called barrier bars. Barrier bar which get keyed up to the headland of a bay is called a spit. When barrier bars and spits form at the mouth of a bay and block it, a lagoon forms. The lagoons would gradually get filled up by sediments from the land giving rise to a coastal plain.

Erosion not only shapes the cliffs but also produces large amounts of sand and gravel. These materials are moved by ocean currents and waves to form beaches and submerged ridges known as bars along the coastline. When these bars extend above the water, they become barrier bars. If they connect to the land, particularly to a headland, they form spits. Over time, if these spits block water bodies like bays, lagoons form. Eventually, these lagoons can fill in with sediment, altering the landscape into flat coastal plains.

Consider a riverbank where sand and pebbles are pushed to one side by flowing water. After a while, this buildup creates a small island or sandbar. Similarly, on high rocky coasts, as waves move materials from the cliffs, they create beaches and other features along the shoreline.

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