Grade 4 · Science · 2 minutes
Weathering and erosion
Weathering breaks it. Erosion moves it. Deposition drops it.
Key terms
- weathering
- The breaking of rock into smaller pieces by roots, wind, water, or ice.
- erosion
- The moving of broken rock pieces to new places by water, wind, ice, and gravity.
- sediment
- Bits of rock, like pebbles and sand, that are carried to new places.
- deposition
- When a river slows down and drops the sediment it was carrying.
- delta
- New land built where sediment piles up in layers, like at the mouth of the Mississippi River.
Transcript
How did a river carve the Grand Canyon, about a mile deep? With help from two powerful teams: weathering and erosion.
Weathering breaks rock into smaller pieces. Plant roots can grow into cracks and pry rocks apart. Sand blown by wind and water scrapes rocks smooth. And rainwater can even slowly dissolve some rocks, like limestone.
But one of the strongest rock breakers is ice. Water seeps into a crack. When it freezes, the ice expands and pushes the crack wider. Then it thaws, more water trickles in, and it freezes again. Freeze, thaw, freeze, thaw, until, crack! The rock splits apart.
Erosion moves the broken pieces away. Water, wind, ice, and gravity all carry rock bits, called sediment, to new places. A fast river can tumble pebbles and sand a long, long way.
When the river slows down, it drops its load. That's called deposition. At the mouth of the Mississippi River, sediment piles up, layer on layer, building brand new land called a delta.
Over millions of years, layers of sediment hardened into rock. Then the Colorado River cut down through them, and carved the Grand Canyon.
In Arches National Park in Utah, water, ice, and wind are still at work, shaping more than two thousand stone arches.
So remember: weathering breaks rock down, erosion carries it away, and deposition drops it somewhere new.
Sources
Every fact in the video, and where it comes from.
- 1nps.gov/grca/learn/photosmultimedia/fly-through.htm
- The Grand Canyon is about a mile deep, 277 miles long and up to 18 miles wide, carved by the Colorado River over about 6 million years.
- 2nps.gov/grca/planyourvisit/upload/life_geology.pdf
- The Grand Canyon's walls are layers of sedimentary rock nearly a mile thick, cut through by the river.
- 3nps.gov/arch/learn/kidsyouth/archformationmovietext.htm
- Arches National Park has over 2,000 documented natural stone arches, shaped by water, ice (freeze-thaw) and wind over time.
- 4earthlearningidea.com/PDF/180_Ice_power.pdf
- Water that seeps into cracks expands as it freezes, widening the crack; repeated freeze-thaw cycles break rock apart (frost/ice wedging).
- 5usgs.gov/centers/spcmsc/science/study-area-and-geologic…
- The Mississippi River delta plain was built by sediment the river deposits where it meets the Gulf, over about 7,000 years.
- 6nextgenscience.org/pe/4-ess2-1-earths-systems
- NGSS 4-ESS2-1: weathering by water, ice, wind, or vegetation, and erosion; deposition where moving water slows.
Image and sound credits
- “Delicate Arch (Arches National Park, eastern Utah, USA) 1 (15512662583)” by James St. John, CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/)
- “Mississippi River Delta (MODIS 2018-11-21)” by MODIS Land Rapid Response Team, NASA GSFC (Public domain)
- “Grand Canyon NP Lipan Point 0016 (5446829074)” by Grand Canyon National Park (Public domain)
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