How fast plates move
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Hawaiian chain (USGS ages; the bend's distance is example data)
Place Age Distance from the Big Island Midway 28 million years 2,600 km The bend 43 million years 3,500 km Northernmost seamounts 80 million years 6,000 km The plate moved 9.3 cm a year from the Big Island to Midway. What was its rate from Midway to the bend, and how does it compare, by Bo's math? (1 km = 100,000 cm.)
- About 6 cm a year, faster than 9.3
- About 60 cm a year, much faster than 9.3
- About 6 cm a year, slower than 9.3
- About 9.3 cm a year, the same as before
The whole chain averages 7.5 cm a year. Why does that differ from the 9.3 and 6 cm a year of two stretches, by Jun's reasoning?
- The 7.5 value is an error, because each stretch must give the same rate
- The stretches are measured in different units, so they cannot be compared
- The 7.5 value was measured by GPS, so it differs from the dated stretches
- An average over 80 million years mixes faster and slower stretches
India moved about 9 m a century, then slowed by about half. India slowed to about 4.5 cm a year, half its earlier rate. How long does it take to move 450 km at that rate, by Kira's math? (1 km = 100,000 cm.)
- About 20 million years
- About 1 million years
- About 10 million years
- About 100 million years
1 cm a year is 10 km per million years. Plate A moves 7 cm a year. Plate B moves 80 km per million years. Which is faster, and by how much, by Luz's math?
- Plate A, by 73 cm a year
- Plate B, by 73 cm a year
- Plate B, by 1 cm a year
- Plate A, by 1 cm a year
GPS measures movement now. Dated stripes and dated volcanoes give rates over millions of years. A team wants a plate's average speed over the last 5 years. Which data fit, by Noah's reasoning?
- GPS station positions over the 5 years
- Dated stripes laid down over millions of years
- The width of the ocean at the ridge today
- The age of one volcano on the plate
The Hawaiian chain's northernmost seamounts are about 80 million years old and about 6,000 km from the Big Island. A team wants a plate's average speed over the last 80 million years. Which data fit, by Pia's reasoning?
- Two GPS readings taken a year apart, one in spring and one in autumn
- The age of the Big Island alone, which is under 0.7 million years
- The ages and distances of the volcanoes along the chain
- The height of Kauai above the sea, compared with that of Midway
Card (example data)
Stripe 1 is 10 million years old and stripe 2 is 14 million years old, 100 km farther from the ridge.
Two stripes are 10 and 14 million years old, and 100 km apart (example). What spreading rate do they give, by Ren's math? (1 km = 100,000 cm.)
- 1 cm a year
- 0.4 cm a year
- 2.5 cm a year
- 0.7 cm a year
Pacific Plate rates by method (USGS)
Method Span Rate GPS today 6 cm a year Midway's age 28 million years 9.3 cm a year Whole chain 80 million years 7.5 cm a year Which statement about the Pacific Plate's rate is supported by the table, by Tala's reading?
- The rate depends on span and method: 6 today, 9.3 over 28 million years, 7.5 over 80
- The rate is 9.3 cm a year, and the other values are measurement errors
- The rate rises with the span, from 6 up to 9.3 cm a year
- The rate is 6 cm a year, since GPS is the sole method that counts
A news item says the Pacific Plate moves 6 cm a year. Which fuller statement fits the table, by Zee's reading?
- Between 6 and 9.3 cm a year, depending on which GPS station is used
- Exactly 6 cm a year at each moment, as GPS shows
- About 9.3 cm a year today by GPS; hotspot ages give 6 to 7.5
- About 6 cm a year today by GPS; hotspot ages give 7.5 to 9.3 over longer spans
The Pacific Plate moves about 6 cm a year today. Midway's age gives about 9.3 cm a year. By about what percent is 9.3 cm a year faster than 6 cm a year, by Ari's math?
- About 55%
- About 3.3%
- About 35%
- About 155%