DK - WOW! The Visual Encyclopedia of Everything

Landscapes are under constant attack

from wind, rain, ice, searing heat, oceanic

waves, and flowing water loaded with

rock fragments. These forces gnaw

away at even the hardest rocks, in

the processes known as erosion and

weathering. Over time they can flatten

the highest mountain ranges, carrying

the rocky debris away as gravel, sand,

and silt. This is deposited in the

lowlands or in the sea – where,

eventually, it may form new rocks.

Erosion

179

◀ RIVER EROSION

Rivers cut V-shaped valleys

and steep-sided gorges,

especially where fast-flowing

water carries a lot of rocky

debris. The most dramatic

gorges form where the land

has been slowly uplifted by

titanic earth movements,

forcing the river to cut deeper

and deeper into the landscape.

KARST TERRAIN

▶

Rainwater is slightly acid, and this

enables it to dissolve limestone.

The result can be a landscape

called karst, with heavily

weathered bare rock riddled

with caves. In tropical areas the

rock is often eroded into

spectacular pinnacles.

SLOT CANYON

▶

Sandy water pours off high mesas

during rare, but torrential desert

rainstorms. It funnels through cracks

in the rock at the edges of the

mesas, eroding them into deep,

winding slot canyons. Unlike valleys,

these are often broader at the

bottom than at the top.

◀ MESAS AND BUTTES

In arid terrain, occasional flash floods

cut down through weak points in the

rock to form valleys. These get wider

and wider, carrying away the softer

rock so the harder layers collapse.

Eventually all that remains are sheer-

sided mesas and smaller buttes, each

protected by a cap of hard rock.

▲ VANISHED GLACIERS

In mountains, and in uplands affected by

the last ice age, huge glaciers grinding along

the courses of former rivers scoured them out

to form deep U-shaped valleys. Where the

glaciers have melted, the valleys remain,

often with small rivers flowing down them.

A beam of sunlight

gleams through

Antelope Canyon, USAthe narrow top of

Rock debris forms steep

scree (rubble) slopes

below the towering

buttes of Monument

Valley, USA

Sharp pinnacles of

limestone form the Stone Forest near

Kunming, China

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