How Glaciers Form

The desire to build structures on coastlines has often interfered with the natural erosion processes. There are many kinds of human-built structures that can be found on coastlines. They include lighthouses, commercial shipping ports, hotels, recreational marinas, and houses.

Protecting human-built structures from coastline erosion has been going on for centuries. Humans have devised many different ways of doing this. Examples include groins, jetties, and breakwaters.

Erosion always has been, and still is, a natural part of the rock cycle. The landforms that you can see along any coastline have evolved naturally over millions of years.

How beaches form

The accumulation of sediment along a coast produces depositional landforms. A beach consists of sand, gravel, or crushed seashells that have been brought to the body of water by rivers and streams, carried by waves, and deposited on the coast.

Streams erode and transport sediment. As the loose sediments are moved along the bottom of the river channel, small bedforms (formations of sediment on the bottom of the stream bed) can develop, such as ripples and sand dunes. The total load (quantity of sediment) of a stream can be described as consisting of three components:

Living things also help form soil. Once rock is weathered into smaller particles, microorganisms and small plants begin to establish themselves there. The microorganisms’ metabolisms release carbon dioxide which readily dissolves in water, forming additional amounts of carbonic acid. The weathering process continues, creating finer particles of new minerals. Below are some examples.

Burrowing animals

This is the decomposition of rocks due to chemical reactions occurring between the minerals in rocks and the environment. The examples below illustrate chemical weathering.

Water

Water, and many chemical compounds found in water, is the main agent of chemical weathering. Feldspar, one of the most abundant rock-forming minerals, chemically reacts with water and water-soluble compounds to form clay.

Acids

Sometimes called mechanical weathering, physical weathering is the process that breaks rocks apart without changing their chemical composition. These examples illustrate physical weathering:

Swiftly moving water

Rapidly moving water can lift, for short periods of time, rocks from the stream bottom. When these rocks drop, they collide with other rocks, breaking tiny pieces off.

Ice wedging

Rock is either broken into smaller particles (disintegration-physical weathering) or altered into other kinds of minerals (decomposition - chemical weathering). Although these processes do not occur in isolation, it is easier to understand them by considering them separately.

Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. In the very hot and pressured conditions deep inside the Earth’s crust, both sedimentary and igneous rocks can be changed into metamorphic rock. In certain conditions these rocks cool and crystallize usually into bands of crystals. Later they can become exposed on Earth’s surface. One way to tell if a rock sample is metamorphic is to see if the crystals within it are arranged in bands.

Rocks are mixtures of one or more minerals. Just like the apples, butter, flour, and sugar are the ingredients of apple pie, minerals like quartz, mica, and feldspar are the ingredients of an igneous (from the Latin word for fire) rock called granite.