rock cycle Flashcards
Rocks can cycle from one type to another over time.
Rocks can cycle from one type to another over time.
Several forces act on the three types of rock to change them from one form to another in the rock cycle.
Weathering breaks exposed rocks of all types into pieces, which can form sedimentary rocks.
Heat and pressure inside the earth can change all types of rocks into metamorphic rocks. They can also melt any type of rock into magma, which forms igneous rocks.
Plate tectonic movements shuttle the rocks between the earth’s interior and surface.
The process of rock formation makes a complete cycle.
From following this rock story, you know that any exposed rock can be made into rock fragments by weathering. Rock fragments erode, are deposited, and become sediment. Sediment accumulates, and heat and pressure change the sediment into rock. With increased heat and pressure, the sedimentary rock turns to metamorphic rock, but it is possible for sedimentary rock to be uplifted and exposed to erosion. In this way, the rock takes a shortcut back to the surface.
Likewise, metamorphic rock can be uplifted to the surface, or it can change to igneous rock if it melts. Even igneous rock can melt, or possibly become a new type of igneous rock through metamorphism.
Explore The Rock Cycle diagram to view the complete process.
Igneous rocks form from molten rock.
Ice that forms from compressed snow will melt if it gets hot enough. The same thing happens to rocks inside the earth.
Rocks melt when they get hot enough and form magma. If the magma erupts, it is called lava. Both lava and magma cool to form rocks.
Lava rocks are exposed to the surface of the earth and begin to weather as soon as they cool. Igneous rocks formed inside the earth from magma are protected from weathering, but tectonic forces push all rocks upward, and erosion of overlying layers exposes the rocks to weathering.
Metamorphic rocks are formed when heat and pressure change other rocks.
Let’s think some more about snow. What happens when the snow continues to accumulate and pack? For example, if you drive a car over snow, it will compress into ice without melting.
Something similar happens to rocks within the earth’s crust. The immense heat and pressure from the overlying rock change existing rocks (igneous, sedimentary, and metamorphic) into metamorphic rocks. Rocks within the crust can also be squeezed as plates push togetherwfor example, during continental-continental convergencewto form mountains.
Sediments get buried in the crust where heat and pressure change them into sedimentary rocks.
Sediment is transported and depositedwby way of gravitywby rivers, streams, and glaciers. Most sediment accumulates on the edge of continents in basins. For example, the Mississippi River carries all its sediment to the Gulf of Mexico, where it accumulates. As the sediment builds, heat, pressure, and cementation turn the sediment into rocks. Lithification is the process of sediment turning into stone.
You may have seen something like this happen when snowflakes become packed snow. When enough snow accumulates, the weight from the overlying snow compresses the flakes together to form a more solid snow mass.
Exposed rocks are subject to weathering and erosion
Wind blows and rain falls on exposed igneous rocks. In time, wind and water break the rock into tiny pieces. Rainfall washes the pieces into rivers and streams where they form sediments.
Over a long period of time, the river flow washes sediments into the sea, where they settle and form layers on the seafloor. Some original igneous rock remains as sedimentary layers in the riverbeds as well. Pressure causes the sedimentary layers to form sedimentary rocks. So, rock that was originally igneous has now been changed.
Heat and pressure melt rocks deep inside the earth.
Heat and pressure within the earth partially melt subducted rocks about 100 km deep. The molten rocks rise and form magma. Some magma rises to the surface and spews out of volcanoes as lava. Other magma never reaches the surface but cools inside the crust just beneath the surface. Regardless of where it cools, magma forms igneous rocks.
Plate tectonics builds mountains and moves rocks.
By way of plate tectonics, rocks move back and forth between the earth’s interior and the surface:
Spreading centers bring magma to the surface.
Subduction causes rocks to sink into the interior.
Subduction also brings magma from the partially melted subducted plate to the surface.
Convergence of continents causes upliftwmountain buildingwthat exposes rocks from underneath.
Mantle plumes (hot spots) bring molten rock from deep within the mantle to the surface.
External forces erode exposed rocks.
Whenever rocks are exposed on the surface, external forces such as wind, ice, and water act on them. These forces break down the rocks in the processes of weathering and erosion. The pieces of eroded rock get washed into bodies of water (rivers, streams, lakes, and oceans) and accumulate there as sediments. As layer upon layer of sediments build up, the pressure converts them into rock in a process called lithification.
The three types of rock form differently.
The three types of rock form differently.
Igneous rock forms when molten rock cools.
intrusive or plutonic: cool while inside the earth
extrusive or volcanic: cool on the earth’s surface
Sedimentary rock forms from existing rock or organisms.
clastic: composed of pieces of eroded rock
chemical: forms from chemical reactions of minerals
organic: made from shells of tiny organisms
