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?

   • 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 column standing out beyond a worn-down cap above
   • 3.5 m further, leaving the cap overhanging the column as in a hoodoo

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?

   • Both belts wear at the same rate, so just their starting heights differ
   • Erosion piles sediment onto the Appalachian peaks, so they stay lower
   • Uplift still feeds the Himalayas, while erosion has worn the Appalachians for over 250 million years
   • 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 2,700 years
   • About 1,600 years
   • About 2,000 years
   • About 270 years
6. 4.

   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 10 million years
   • About 100 billion years
7. 5.

   NPS dates the Colorado Plateau uplift to 70–30 million years ago and the river's carving to the last 5–6 million years. Pia finds the gap between them.

   • About 64 to 65 million years: from the start of uplift to the start of carving
   • About 24 to 25 million years: uplift ended well before the carving began
   • No gap: the river cut the canyon while the plateau was rising
   • About 40 million years: the span of the uplift itself, from 70 to 30

8. 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

9. 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
   • 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
   • Kauai is lower because lava did not build it; erosion did
10. 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 3 to 3.7 mm a year
    • About 300 to 370 mm a year
    • About 0.03 to 0.04 mm a year
    • About 0.30 to 0.37 mm a year

11. 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

12. 8.

    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 600 m: it gains 800 m while A gains 200 m
    • Range B, by 800 m: its own net gain over the period
    • Neither: they rise at the same rate, so they end equal
13. 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?

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

14. 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.

15. 10.

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

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