Page 268 - Ultimate Visual Dictionary (DK)

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

The rock cycle

THE ROCK CYCLE IS A CONTINUOUS PROCESS through which old rocks are transformed
into new ones. Rocks can be divided into three main groups: igneous, sedimentary, and
metamorphic. Igneous rocks are formed when magma (molten rock) from the Earth’s
interior cools and solidifies (see pp. 274-275). Sedimentary rocks are formed when
sediment (rock particles, for example) becomes compressed and cemented together
in a process known as lithification (see pp. 276-277). Metamorphic rocks are formed
when igneous, sedimentary, or other metamorphic rocks are changed by heat or
pressure (see pp. 274-275). Rocks are added to the Earth’s surface by crustal movements
and volcanic activity. Once exposed on the surface, the rocks are broken down into rock
particles by weathering (see pp. 282-283). The particles are then transported
HEXAGONAL BASALT by glaciers, rivers, and wind, and deposited as sediment
COLUMNS, ICELAND
in lakes, deltas, deserts, and on the ocean floor. Some STAGES IN THE ROCK CYCLE
of this sediment undergoes lithification and forms sedimentary rock.
Magma extruded as lava,
This rock may be thrust back to the surface by crustal movements or which solidifies to form
forced deeper into the Earth’s interior, where heat and pressure igneous rock
transform it into metamorphic rock. The metamorphic rock in
Lava
turn may be pushed up to the surface or may be melted to Vent flow
form magma. Eventually, the magma cools and solidifies- Main
below or on the surface-forming igneous rock. When the conduit
sedimentary, igneous, and metamorphic rocks Secondary
are exposed once more on the Earth’s surface, the conduit
cycle begins again.
THE ROCK CYCLE
Lava

Igneous Ash
rock Weathering, transport, Sediment
Cooling and solidification (crystallization)
and deposition

Magma Heat and pressure (metamorphism) Weathering, transport, and deposition Weathering, transport, and deposition Compression and cementation (lithification)

Melting Rock surrounding
magma changed
Heat and pressure by heat to form
(metamorphism) metamorphic rock
Sedimentary rock
Metamorphic Sedimentary
rock rock crushed and folded to
Intense heat of rising form metamorphic rock
magma melts some of
the surrounding rock
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