Worksheet

Kestrel Falls After the Rain: Forecasting Landslides on a Mountain Road

Grade 7 earth science: a mountain town uses storm records, earthquake data and a crack meter to forecast landslides and pick safety projects.

Grade 7ScienceInteractive · Printable

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1 NGSS standard
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11 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

Students analyze storm and earthquake records to find conditions that set off landslides.
Students use monitoring data to forecast when a slope may fail.
Students judge which technologies forecast landslides and which reduce their damage.

How to use

Read the town hall notes together, then let students find the rain levels in Table 1 on their own before discussing the forecasts. Section 3 works well as a small-group decision.

Curriculum

NGSS standard covered

MS-ESS3-2

Use data on natural hazards to forecast future events and inform technologies that reduce their effects.

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Kestrel Falls After the Rain: Forecasting Landslides on a Mountain Road

Use storm, earthquake and crack-meter data to forecast landslides and choose ways to reduce the danger.

Rain and landslides

Read the town hall notes and Table 1, then answer the questions.

Town Hall Notes: The Slopes Above Kestrel Falls

1Kestrel Falls is a mountain town of about 6,000 people in a narrow river valley. The only road into town, Switchback Road, zigzags up a steep hillside, and landslides have closed it several times. Hillside School sits at the foot of another slope on the east side of town. This fall, the town's hazard team, led by engineer Ms. Ilona Brzezinski, invited seventh graders Joaquín Teller and Saoirse Mbatha-Klein from the school's science club to help plan for the next landslide season.

2A landslide is a mass of soil and rock that slides downhill. On a slope, gravity pulls the soil downhill, while friction between grains and the roots of plants help hold it in place. Steep slopes slide more easily than gentle ones. When heavy rain soaks into the ground, water fills the spaces between grains, adds weight and pushes the grains apart, so they grip each other less firmly. Strong shaking during an earthquake can also jar soil and rock loose. Small earthquakes are common in this region, and a large one strikes every few decades.

3The team began with the ten largest storms of the past 20 years (Table 1). For each storm, it recorded the total rain in 48 hours and whether the ground was already wet from rain during the week before.

4Next, the team studied a magnitude 6.3 earthquake that shook the region in 2009. Geologists had checked 160 slopes after it and sorted them by how steep they are (Table 2).

5Last, the team looked at a crack across the top of the slope above Hillside School. In August, the crew strung a crack meter, a wire that measures how much the crack opens, across it. Before a slope slides, it often creeps slowly at first, and the creeping speeds up as the slide gets close.

Table 1. The ten largest storms in 20 years
Storm	Ground before storm	Rain in 48 h (mm)	Landslides on road?
1	Dry	40	No
2	Wet	50	No
3	Dry	75	No
4	Wet	65	Yes
5	Dry	90	No
6	Wet	140	Yes
7	Dry	120	Yes
8	Wet	80	Yes
9	Dry	110	Yes
10	Wet	30	No

Which statement best describes the pattern in Table 1?

A. Landslides came with heavy rain, and less rain set them off when the ground was already wet.
B. Landslides came with heavy rain, and more rain was needed when the ground was already wet.
C. Landslides came after storms on wet ground, but the amount of rain made little difference.
D. Landslides came after about half of the storms, with no clear link to rain or wet ground.

Use Table 1. Find the smallest amount of rain that set off landslides in each kind of storm.

On dry ground: mm in 48 h
On wet ground: mm in 48 h

After a rainy week, the weather service forecasts 70 mm of rain in the next 48 hours. Which action is best supported by Table 1?

A. Keep the road open, since no storm in Table 1 had exactly 70 mm of rain.
B. Wait to warn drivers until a slide has blocked the road, since slides come after storms.
C. Keep the road open, since storms on dry ground needed more than 100 mm to cause slides.
D. Warn drivers about the road, since storms of 65 mm or more on wet ground caused slides.

Use paragraph 2. Why does wet ground need less new rain to slide?

A. The new rain runs off wet ground faster, so it carries the road away.
B. Its spaces already hold water, so a little more rain loosens the grains.
C. Wet ground is colder, so the soil freezes and cracks apart.
D. Wet ground makes plant roots grow faster and push the soil downhill.

Earthquakes and a creeping slope

Use Tables 2 and 3 and paragraphs 4 and 5.

Table 2. Slopes checked after the 2009 earthquake
Steepness of slope	Slopes checked	Slopes that slid
Less than 15°	40	0
15° to 30°	40	4
30° to 40°	40	14
More than 40°	40	26

What percent of the slopes steeper than 40° slid in 2009? %

The slope above Hillside School is about 35° steep. The slope behind the town library is about 10° steep. Suppose another earthquake like the one in 2009 strikes. Which forecast is best supported by Table 2?

A. The school slope is more likely to slide, since about a third of 30° to 40° slopes slid.
B. Neither slope is likely to slide, since most of the 160 slopes checked held.
C. The library slope is more likely to slide, since gentle slopes hold more loose soil.
D. Both slopes are about equally likely to slide, since they would feel the same shaking.

Table 3. Crack meter above Hillside School
Week	Total opening (mm)
0	0
1	1
2	2
3	3
4	5
5	9
6	17

How many millimeters did the crack open during week 6 alone, from week 5 to week 6? mm

Use paragraph 5 and Table 3. What should the hazard team conclude?

A. The crack opened about 1 mm each week, so the slope is creeping at a steady, slow rate.
B. The weekly opening has doubled each week since week 3, so a slide may be close.
C. The crack opened most in the first weeks, so the slope is settling down.
D. The crack is less than 2 cm wide, so the slope above the school is stable.

Reducing the danger

Use what you learned to judge the town's plans.

Sort each technology by its main job.

Rain gauges that text drivers when the 48-hour rain passes a danger levelPipes drilled into the slope to drain water out of the soilA crack meter that sounds an alarm when the crack opens quicklyDeep-rooted shrubs planted across a bare slopeA weather forecast app that shows the rain expected in the next 48 hoursA steel-and-rock wall that holds the bottom of the slope in place

Forecasts or warns of a landslide	Makes a slope less likely to slide

The town will fix the worst slope on Switchback Road. A computer model of each project tested the slope with wet ground.

Table 4. Projects for Switchback Road
Project	Most rain held (mm/48 h)	Cost ($ million)	Time to finish
A. Deep-rooted shrubs	90	0.2	5 years
B. Drain pipes	150	1.5	6 months
C. Concrete wall	160	6	2 years
D. Wire net over slope	100	0.8	4 months

The town's criteria: 1. The slope holds through a storm as large as Storm 6. 2. The project costs no more than $3 million. 3. It is finished within 1 year.

10.

Which project meets all three criteria?

A. C. Concrete wall
B. A. Deep-rooted shrubs
C. B. Drain pipes
D. D. Wire net over slope

11.

A council member says, "Landslides strike at random, so nobody can forecast them. Rain gauges and crack meters are a waste of money." Do you agree? Make a claim, use evidence from at least two of the tables, and explain your reasoning about how forecasts and technology work together.