About rock cycle

Solid as a rock: Have you heard someone say that before? Rocks have a reputation for being solid, hard, and indestructible. Rocks line river beds and jut above the landscape as mountain peaks; they are fun to collect and sometimes are very beautiful. Each rock is different – some are smooth and round, some are sharp and dangerous. They come in all colors: pink, green, orange, white, red. They are everywhere, and we take their presence for granted and assume that they are unchangeable.

But rocks are not unchangeable! Just like the water cycle, rocks undergo changes of form in a rock cycle. A metamorphic rock can become an igneous rock, or a sedimentary rock can become a metamorphic one. Unlike the water cycle, you can't see the process happening on a day-to-day basis. Rocks change very slowlyunder normal conditions, but sometimes catastrophic events like a volcanic eruption or a flood can speed up the process. So what are the three types of rocks, and how do they change into each other? Keep reading to find out!

Weathering & Erosion. Igneous, sedimentary, and metamorphic rocks on the surface of the earth are constantly being broken down by wind and water. Wind carrying sand wears particles off rock like sandpaper. Rushing river water and crashing surf rub off all the rough edges of rocks, leaving smooth river rocks or pebbles behind.

Water seeps into the cracks in mountain rocks, then freezes, causing the rocks to break open. The result of all this: large rocks are worn down to small particles. When the particles are broken off a rock and stay in the same area, it is called weathering. When the particles are carried somewhere else, it is called erosion.

Transportation. Eroded rock particles are carried away by wind or by rain, streams, rivers, and oceans. Deposition. As rivers get deeper or flow into the ocean, their current slows down, and the rock particles (mixed with soil) sink and become a layer of sediment. Often the sediment builds up faster than it can be washed away, creating little islands and forcing the river to break up into many channels in a delta.

Compaction & Cementation. As the layers of sediment stack up (above water or below), the weight and pressure compacts the bottom layers. (Try making a stack of catalogs and watch how the bottom one gets squished as you add more on top – this is the same idea as the compaction of layers of sediment.) Dissolved minerals fill in the small gaps between particles and then solidify, acting as cement. After years of compaction and cementation, the sediment turns into sedimentary rock.

Metamorphism. Over very long periods of time, sedimentary or igneous rocks end up buried deep underground, usually because of the movement of tectonic plates. While underground, these rocks are exposed to high heat and pressure, which changes them into metamorphic rock.