40 Fun Facts About Erosion

Which river carved Arizona's Grand Canyon, cutting through a mile of rock in five to six million years?

The Colorado did not work alone: side streams and collapsing cliffs widened the canyon to as much as 18 miles across.

What name was given to the 1930s disaster in which wind stripped bare topsoil from the American Great Plains?

Dust Bowl was coined by an Associated Press editor after the Black Sunday storms of April 1935, and the damage reached about 100 million acres.

Which famous waterfall has retreated almost seven miles upstream since the last ice age by wearing away its own ledge?

Niagara Falls once wore back more than three feet a year; engineering works have slowed that to about one foot.

Which is missing from the Moon, along with liquid water, so that weather never wears away the Apollo bootprints?

An atmosphere would bring wind and rain; without one, the Moon's surface is worn only by micrometeorites that slowly soften and round its features.

Which Chinese waterway picks up so much silt crossing the Loess Plateau that its rising bed causes disastrous floods?

Yellow River water gets its color, and the river its name, from that silt, which settles on the bed and slowly builds natural dams.

Which John Steinbeck novel follows the Joads, an Oklahoma farm family driven out by 1930s drought and blowing soil?

The Grapes of Wrath sends the Joads west to California after failed crops cost them the farm, and it won the Pulitzer Prize for fiction.

England's White Cliffs of Dover, which shed large slabs into the Channel, are made of which soft white rock?

Chalk at Dover is streaked with bands of black flint, and it began as white mud made of the skeletons of tiny algae that settled on a Cretaceous seabed.

Which force drives landslides, rockfalls and mudflows, the downhill movements geologists group together as mass wasting?

Gravity needs no river, wind or ice to carry the load, which is what sets mass wasting apart from every other kind of erosion.

Which icicle-like formation grows down from a cave ceiling as dripping water leaves behind dissolved minerals?

Stalactite was coined in the 17th century by the Danish physician Ole Worm, who built the word from the Greek for dripping.

Which hazard, common in central Florida, opens when buried rock dissolves and the ground above suddenly gives way?

Sinkhole collapses are not limited to Earth: in 2015 the Rosetta probe found similar pits on comet 67P/Churyumov-Gerasimenko.

Which of the main kinds of weathering changes what a rock is made of, as when acid rain dissolves stone?

Chemical weathering is why statues, monuments and ornamental stonework can be badly damaged simply by standing outdoors in the rain.

Which type of weathering splits rock when water trapped in its cracks swells by about nine percent on cold nights?

Frost wedging needs the crack to be full of water and to freeze quickly from all sides, so the pressure pushes on the rock instead of escaping.

Which gas dissolves in ordinary rainwater to make the weak acid that slowly eats away cave-forming rock?

Carbon dioxide turns even unpolluted rain into carbonic acid with a pH of about 5.6, acidic enough to dissolve solid rock given time.

Which rock, built largely from shells and skeletons of sea life, dissolves in rainwater to form most cave systems?

Limestone is only slightly soluble, so the work is slow, but where it lies exposed over large regions whole landscapes of caverns develop.

Which term for a landscape of caves and vanishing streams comes from a rocky plateau near the Italian port of Trieste?

Karst reached European scholars in 1689, when Johann Weikhard von Valvasor used the word to describe rivers flowing underground at Lake Cerknica.

Which reaction between iron-bearing minerals, water and the air leaves rock surfaces reddish-brown and crumbly?

Oxidation is the same reaction that rusts a nail, and the iron compounds it leaves in rock include hematite and goethite.

Which crusty organisms, among the first living things to settle on bare rock, slowly turn the stone into soil?

Lichens pry mineral grains loose with rootlike threads and then break the fragments down inside their bodies, a process compared to digestion.

Which weathering process, peeling rock away in curved sheets like onion layers, rounded the granite domes of Yosemite?

Exfoliation starts with relief from pressure: once erosion strips away the rock above, long-buried granite cracks in shells parallel to its surface.

Which hard mineral, slow to break down, makes up most of the sand on beaches outside the tropics?

Quartz outlasts its neighbors: in granite the feldspar dissolves faster, so the rock crumbles and the tougher grains are left behind as sand.

Which fine, sticky material is the main product when the feldspar in granite slowly breaks down in water?

Clay of one kind, kaolinite, forms in abundance in hot, moist climates, and the name kaolin reached English through French reports on Chinese porcelain making.

Which landform, like the one where the Mississippi meets the sea, is built from mud a river drops at its mouth?

Delta was what the Ionian Greeks called the triangle of silt at the mouth of the Nile, a name Herodotus used fourteen times in his Histories.

Which crescent lake is left behind when a winding river cuts through the neck of one of its own loops?

Oxbow lakes are called billabongs in Australia, and one is complete once silt plugs both ends of the abandoned loop.

Which word for a river's looping bend comes from a famously winding river in Asia Minor known to the ancient Greeks?

Meander comes from the Maiandros, today's Menderes in Turkey; the geographer Strabo wrote that everything winding was named after its course.

Which cross-section, named for a letter, does a mountain glacier leave when it scours a river valley into a trough?

U-shaped troughs take time: remaking the V-shaped valley a river has cut can occupy a glacier for anywhere from 10,000 to 100,000 years.

Which long, steep-sided sea inlet, found by the hundred along Norway's coast, fills a valley gouged out by a glacier?

Fjord coasts are so crinkled that Norway's shoreline measures about 18,000 miles with its inlets counted and only 1,600 miles without them.

Which ridge of boulders, gravel and grit marks where a glacier dumped the debris it had been carrying?

Moraine reached English from French, which took it from a Savoyard word for a mound of earth; the debris runs from fine rock flour to large boulders.

Which Swiss–Italian border mountain is the classic pyramid peak, sharpened by glaciers biting in from several sides?

The Matterhorn has four steep faces cut by glaciers hollowing out basins around it, and four of the seven who first climbed it in 1865 died descending.

Which landform, common in Death Valley, spreads out where a canyon stream reaches flat ground and drops its gravel?

Alluvial fan deposits are not unique to Earth: they have been found in abundance on Mars and on Saturn's moon Titan.

Which bank builds up naturally beside a river as each flood drops its coarsest sand and gravel first?

Levee comes from the French for raised, and French settlers in Louisiana began building artificial ones in the 18th century to protect New Orleans.

Which erosion process works like sandpaper, as grit carried by wind, waves, rivers or ice grinds against solid rock?

Abrasion is at its most patient under a glacier, where rocks picked up by the ice are slowly ground against the bedrock below.

The Twelve Apostles off Victoria, Australia, are which kind of rock pillar, left standing when wave-cut arches collapse?

Stacks do not last long in geological terms: one 50-metre pillar in the group crumbled into the sea in July 2005.

What are the tall, thin rock spires that crowd Bryce Canyon National Park more thickly than anywhere else called?

Hoodoos are known in French as fairy chimneys, and in the Cappadocia region of Turkey people carved whole houses into them.

Which farming method, used for Asian rice paddies and by the Inca in the Andes, cuts level steps into steep hillsides?

Terracing in the Andes is older than the Inca: the Wari and their neighbors built stepped fields before 1000 AD, and the Inca adopted them.

Which soil-saving practice has farmers work across a slope along lines of equal elevation instead of up and down it?

Contour plowing and other new techniques had cut soil loss by 65 percent by 1938, even though the drought of the 1930s was still going on.

Which US president launched the 1934 Great Plains Shelterbelt, a band of tree windbreaks from Canada to Texas?

Franklin Roosevelt's project paid farmers to plant and tend the trees, and by 1942 it had put 220 million of them in the ground.

Which coastal process shifts sand sideways along a beach because waves usually reach the shore at an angle?

Longshore drift works in zigzags: each wave carries sand up the beach at a slant, and the backwash pulls it straight back down.

Which term, from the Latin for leap, describes sand grains bouncing along the ground in a strong wind?

Saltation is not limited to desert sand: the same hopping motion carries pebbles down rivers and wind-blown snow across the Canadian Prairies.

Which keeper of the winds in Greek myth gives geologists their word for landforms sculpted by moving air?

Aeolus lends his name to aeolian processes, which matter most in deserts, even though water is a far more powerful eroding force than wind.

What name do geologists give the layer of loose rock fragments and soil lying on top of solid bedrock?

Regolith joins the Greek words for blanket and rock, and spacecraft have found the same loose covering on asteroids such as Eros.

What name is given to a wire basket packed with stones and piled along riverbanks to stop the soil washing away?

Gabion comes from the Italian for big cage, and Leonardo da Vinci designed one for the foundations of the Sforza Castle in Milan.