Forces that build land up and wear it down

Grade 9 Science Worksheet

Circle the best answer.

1. 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

2. 1.

   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
   • 3.5 m further, leaving the cap overhanging the column as in a hoodoo
   • 35 cm further, leaving the cap overhanging the softer column below

3. Two mountain belts

   Belt	Highest peak (m)	Plate collision
   Himalayas	8,849	still pushing today
   Appalachians	2,037	ended over 250 million years ago

4. 2.

   Jun compares the belts. Which explanation of the height difference fits the table best?

   • Uplift still feeds the Himalayas, while erosion has worn the Appalachians for over 250 million years
   • Erosion piles sediment onto the Appalachian peaks, so they stay lower
   • Both belts wear at the same rate, so just their starting heights differ
   • Weathering is faster in the Himalayas, so it builds them higher
5. 3.

   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

6. 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

7. 4.

   Milo spreads the net sediment evenly over the delta. By how much does its surface rise each year?

   • About 0.5 cm a year
   • About 5 cm a year
   • About 20 cm a year
   • About 35 cm a year
8. 5.

   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 100,000 years
   • About 100 million years
   • About 100 billion years
   • About 10 million years

9. 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

10. 6.

    Ren compares the islands. Which explanation of their heights fits the table best?

    • Kauai is lower because it is younger than the Big Island
    • Kauai is lower because lava did not build it; erosion did
    • The Big Island is higher because erosion has worn it more
    • Lava still builds the Big Island up, while erosion has lowered Kauai for about 5 million years
11. 7.

    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 300 to 370 mm a year
    • About 0.30 to 0.37 mm a year
    • About 3 to 3.7 mm a year

12. 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

13. 8.

    Esme runs both ranges for 1 million years. Which range ends higher, and by how much?

    • Range B, by 600 m: it gains 800 m while A gains 200 m
    • Neither: they rise at the same rate, so they end equal
    • Range A, by 600 m: wet, freezing air builds more rock
    • Range B, by 800 m: its own net gain over the period
14. 9.

    A range 3,000 m high kept its height for 10 million years while erosion removed 0.5 mm a year. What uplift rate does Zee say that needs?

    • Zero: an unchanged height means no process is acting
    • About 0.05 mm a year, adding 500 m over 10 million years
    • About 0.5 mm a year, adding 5,000 m of rock over 10 million years
    • About 0.3 mm a year, adding the 3,000 m height in 10 million years

15. 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.

16. 10.

    Ari reads the table. Which explanation fits the falling erosion rate?

    • Lower, gentler slopes give water less energy to cut and carry rock
    • Weathering stops once uplift stops, so nothing is left to carry away
    • Erosion piles rock back onto the range, so less is removed
    • Lower ranges receive more sunlight, which slows erosion