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TerraPrinter Classroom · Worksheet · Ages 11–16

Plate boundaries and rift valleys

Name Class Date

At a divergent plate boundary, two plates move apart. The ground between them stretches, cracks and drops down, making a rift valley. Use the models of Þingvellir in Iceland and the East African Rift in Kenya.

You need these models

Open a link in a web browser to see the model in 3D, or use the printed model from your teacher.

  1. Which two plates meet at Þingvellir?

  2. Sketch a cross-section across the Þingvellir valley. Label: valley floor, fault scarp, and arrows showing which way each plate moves.

  3. The plates here move apart about 2 cm a year. How far will they move apart in 1,000 years? In 1 million years?

  4. Find the edge of the large lake at the south of the Þingvellir model. Why do lakes often form in rift valleys?

  5. The Kenya model is 150 mm across for 80 km. Measure the width of the rift floor in mm, then work out its real width: (mm ÷ 150) × 80 km.

  6. The Kenya model is drawn 3× taller than true scale. Why was this done? What wrong idea could it give people?

  7. Mount Longonot is a volcano inside the Kenyan rift. Why does magma rise where plates pull apart?

terraprinter.com/classroom/worksheet/rift-valleys/

TerraPrinter Classroom, CC BY 4.0: free to copy and adapt with credit.

TerraPrinter Classroom · For the teacher

Answer key: Plate boundaries and rift valleys

Learning goals

Answers

  1. Which two plates meet at Þingvellir?The North American plate (to the west) and the Eurasian plate (to the east).
  2. Sketch a cross-section across the Þingvellir valley. Label: valley floor, fault scarp, and arrows showing which way each plate moves.A lower, fairly flat floor between two steps or cliffs (fault scarps), with arrows on each side pointing away from the middle. The big western scarp is Almannagjá.
  3. The plates here move apart about 2 cm a year. How far will they move apart in 1,000 years? In 1 million years?1,000 years: 2,000 cm = 20 m. 1 million years: 20 km.
  4. Find the edge of the large lake at the south of the Þingvellir model. Why do lakes often form in rift valleys?The valley floor is low and keeps sinking, so rivers and groundwater flow into it and the water collects. The lake is Þingvallavatn, the largest natural lake in Iceland.
  5. The Kenya model is 150 mm across for 80 km. Measure the width of the rift floor in mm, then work out its real width: (mm ÷ 150) × 80 km.Answers depend on the measurement. For example, 60 mm ÷ 150 × 80 = 32 km. The rift here is a few tens of kilometres wide, far wider than at Þingvellir.
  6. The Kenya model is drawn 3× taller than true scale. Why was this done? What wrong idea could it give people?At true scale, 1 mm on this print is about 530 m, so walls a few hundred metres high would be barely 1 mm tall. Exaggeration makes them visible, but makes the slopes look much steeper than they really are.
  7. Mount Longonot is a volcano inside the Kenyan rift. Why does magma rise where plates pull apart?As the crust stretches it gets thinner, so there is less pressure on the hot mantle rock below. Some of it melts, and the magma rises up through the cracks.

Before the lesson

Print the models at 150 mm wide, 0.2 mm layers, 10–15% infill, no supports. The Kenyan rift is 80 km across, so its walls are drawn 3× taller than true scale to show up in print; Þingvellir uses 2×. Talk about this exaggeration with the class. Measurements on the sheet assume the 150 mm size. Students' measured answers will vary a little with how they measure. Discussion questions and a hands-on activity for this topic: terraprinter.com/classroom/#rift-valleys