Forces that build land up and wear it down
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Retreat of two layers (example data)
Layer Rock Retreat per 1,000 years Cap hard limestone 5 cm Column soft siltstone 40 cm Bo projects 10,000 years ahead. How much further has the soft rock retreated than the cap, and what shape results?
- 3.5 m further, leaving the column standing out beyond a worn-down cap above
- 4 m further, leaving the cap overhanging the column
- 35 cm further, leaving the cap overhanging the softer column below
- 3.5 m further, leaving the cap overhanging the column as in a hoodoo
Two mountain belts
Belt Highest peak (m) Plate collision Himalayas 8,849 still pushing today Appalachians 2,037 ended over 250 million years ago Jun compares the belts. Which explanation of the height difference fits the table best?
- Erosion piles sediment onto the Appalachian peaks, so they stay lower
- Weathering is faster in the Himalayas, so it builds them higher
- Uplift still feeds the Himalayas, while erosion has worn the Appalachians for over 250 million years
- Both belts wear at the same rate, so just their starting heights differ
Luz studies a cliff where nights often freeze and rock fragments pile at the base. Which observation best supports frost wedging as the main weathering?
- A fan of sediment 5 km away at a river mouth
- Rounded pebbles lying in a stream bed nearby
- Rock faces coated with a soft, clay-rich crust
- Sharp-edged fragments with fresh, unaltered faces piled at the cliff base
Kira studies a field with 40 cm of soil. Weathering makes 0.05 mm of soil a year and erosion strips 0.2 mm (example data). If rates hold, how long until bare rock?
- About 2,000 years
- About 2,700 years
- About 270 years
- About 1,600 years
Delta budget (example data)
Item Amount Sediment from the river 12 million m³ a year Sediment removed by waves 9 million m³ a year Delta area 60 km² Milo spreads the net sediment evenly over the delta. By how much does its surface rise each year?
- About 5 cm a year
- About 20 cm a year
- About 35 cm a year
- About 0.5 cm a year
Noah models a 2,000 m range that stops rising. Erosion lowers it 0.02 mm a year (example data). About how long until it is worn flat?
- About 100 million years
- About 100 billion years
- About 100,000 years
- About 10 million years
Two Hawaiian islands
Island Age of oldest rock Highest point (m) Erupting now Kauai about 5 million years 1,598 no Hawaii (Big Island) under 1 million years 4,207 yes Ren compares the islands. Which explanation of their heights fits the table best?
- Kauai is lower because lava did not build it; erosion did
- Kauai is lower because it is younger than the Big Island
- Lava still builds the Big Island up, while erosion has lowered Kauai for about 5 million years
- The Big Island is higher because erosion has worn it more
NPS gives the Grand Canyon's greatest depth as about 1,829 m, cut in 5–6 million years. Tala finds the average cutting rate in mm a year.
- About 0.03 to 0.04 mm a year
- About 3 to 3.7 mm a year
- About 300 to 370 mm a year
- About 0.30 to 0.37 mm a year
Two ranges (example data)
Range Climate Uplift (mm/yr) Erosion (mm/yr) A wet and freezing 1.0 0.8 B dry and mild 1.0 0.2 Esme runs both ranges for 1 million years. Which range ends higher, and by how much?
- Range A, by 600 m: wet, freezing air builds more rock
- Range B, by 800 m: its own net gain over the period
- Neither: they rise at the same rate, so they end equal
- Range B, by 600 m: it gains 800 m while A gains 200 m
Use this
Table, Erosion rate as a range wears down (example data), with columns Time since uplift stopped, Height (m), Erosion rate (mm/yr): 0 years, 4,000, 1.0; 50 million years, 2,000, 0.3; 150 million years, 600, 0.05.
Ari reads the table. Which explanation fits the falling erosion rate?
- Erosion piles rock back onto the range, so less is removed
- Lower, gentler slopes give water less energy to cut and carry rock
- Lower ranges receive more sunlight, which slows erosion
- Weathering stops once uplift stops, so nothing is left to carry away