Worksheet

Thin Soil, Strong Springs: Finding Resources in Tamarack Gap

Grade 7 earth science: soil pits, spring flows and tilted rock layers explain why soil and groundwater are spread unevenly in a mountain valley.

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13 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Short answer

About this worksheet

What students practice

Students use soil pit data to explain how weathering, landslides and floods leave soil thin or thick.
Students explain how rock layers, their tilt and a fault control where springs flow and how strongly.
Students use the processes to choose places for a farm and a water source.

How to use

Read paragraphs 1 and 2 with Table 1 first and answer section 1, then read paragraph 3 for the springs. A quick sketch of the two tilted layers on the board helps before question 8.

Curriculum

NGSS standard covered

MS-ESS3-1

Explain how geoscience processes cause the uneven distribution of minerals, energy and groundwater resources.

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Thin Soil, Strong Springs: Finding Resources in Tamarack Gap

Use soil pits and spring flows to explain why a mountain valley's resources are uneven.

Where the soil is

Read the survey notes and Table 1, then answer the questions.

Survey Notes: Soil and Water in Tamarack Gap

1Tamarack Gap is a town of about 3,000 people in a steep mountain valley in the western United States. Small earthquakes rattle the valley a few times a year, and a fault, a long break in the rock where huge blocks slip past each other, runs along the east side of the valley floor. In 2019, a landslide came down the west side of the valley and broke the pipe that carried the town's water from Spring S1. Now the town council wants a safer water source and land for a community farm. Geologist Mr. Anselm Takeda asked two seventh graders, Odette Kariuki and Bruno Ferraz, to help him survey the valley.

2Soil forms where frost, plant roots and water break bedrock into small grains, and dead plants rot and mix in. On these slopes, bedrock turns into soil at about 0.1 mm a year. Gravity also moves soil downhill, slowly as it creeps a little each year and suddenly in landslides. During floods, the river spreads mud and sand over the valley floor. The team dug five soil pits and measured how thick the soil was (Table 1). Pit C is in the bare scar the 2019 landslide left behind, and Pit D is in the pile of soil and broken rock the landslide dropped at the foot of the slope. The soil in Pit E is made of many thin layers of silt and sand.

3The valley sides are made of two rock layers. The upper layer is sandstone, which has connected spaces between its sand grains, so water moves through it easily. Under it lies shale, made of tightly packed clay, which water can barely move through. The boundary between the two layers is at about 1,450 m above sea level on both sides of the valley. On the west side, the layers tilt gently down toward the valley. On the east side, they tilt gently down away from the valley. Rain and snowmelt soak into the sandstone on the high ridges. Along the fault, earthquakes over many thousands of years have ground the shale into broken, crushed rock. The team measured the flow of every spring in the valley (Table 2). Apart from Spring S4, no water comes out of the shale anywhere in the valley.

Table 1. Soil pits in the valley
Pit	Place	Slope (°)	Soil thickness (cm)
A	Flat ridge top	3	40
B	Steep upper slope	35	10
C	2019 landslide scar	32	0
D	Landslide pile at foot of slope	10	180
E	Valley floor near river	1	250

Which statement best describes the pattern in Table 1?

A. Soil is about 40 cm thick in each pit, except where the 2019 landslide hit.
B. Soil is thin on steep slopes and thickest low down, where soil has piled up.
C. Soil gets thinner going down the valley, so the ridge top has the most soil.
D. The steeper the place, the thicker its soil, so Pit B has more soil than Pit A.

Pits A and E are both on nearly flat ground. Why is the soil in Pit E more than 6 times as thick?

A. The ridge top gets too little rain for its bedrock to start breaking into grains.
B. Small earthquakes shake most of the ridge-top soil down into the river each year.
C. Floods have spread soil from upstream over it, while Pit A has only soil made in place.
D. Pit E was dug deeper into the ground than Pit A, so it reached more soil.

Circle every pit where most of the soil was carried in from somewhere else.

Pit APit BPit CPit DPit E

The 2019 landslide dropped the 180 cm (1,800 mm) of soil in Pit D in a few minutes. Suppose that much soil had to form in place from bedrock at the rate in paragraph 2.

It would take about years to form.

The town wants land for a community farm with soil at least 1 m thick. Where should it look first?

A. On the flat ridge tops, where soil forms in place and no landslides reach
B. On the valley floor and gentle land at the foot of slopes, where soil has collected
C. In the 2019 landslide scar, where the slide has cleared away rocks and trees
D. On the steep upper slopes, where the bedrock is closest to the surface

Where the water comes out

Use paragraph 3 and Table 2 to answer the questions.

Table 2. Springs in the valley
Spring	Side of valley	Height (m)	Where it comes out	Flow (L/min)
S1	West	1,450	Bottom of sandstone	120
S2	West	1,440	Bottom of sandstone	96
S3	East	1,450	Bottom of sandstone	8
S4	East	1,250	Crushed rock at fault	60

Use paragraph 3 and Table 2. Which statement best describes where the springs are?

A. The springs are found on the east side, where the fault runs along the valley.
B. Most come out of the middle of the shale, far below the bottom of the sandstone.
C. The springs come out at many heights, from the ridge tops down to the river.
D. Three come out where sandstone sits on shale, and one comes out along the fault.

Spring S2 gives times as much water per minute as Spring S3.

Why do Springs S1, S2 and S3 come out at about 1,450 m?

A. Shale makes new water when the heavy sandstone above squeezes it.
B. Water rises up through the shale and spills out at its upper edge.
C. Water soaks down through sandstone, and shale stops it and sends it sideways.
D. Sandstone holds no water, so rain runs down over it until it reaches shale.

Springs S1 and S3 come out of the same layers at the same height. Why does S1 give 15 times as much water?

A. The west-side layers tilt toward the valley, so water along the shale flows out there.
B. The sandstone on the east side has no spaces between its grains for water.
C. S3 is lower in the valley, so less of the water from the ridges reaches it.
D. Earthquakes on the fault shook the water out of the east-side sandstone.

10.

Water can barely move through shale, yet Spring S4 comes out of the shale. Which explanation fits paragraph 3 best?

A. Movement on the fault crushed the shale, which opened cracks that water can flow through.
B. The shale along the fault has turned back into sandstone after many earthquakes.
C. The fault is lower than the other springs, so it is closer to an underground lake.
D. Each earthquake makes new water deep in the fault, which then rises to the surface.

Choosing the new water line

Use Table 3, the council's two needs and the survey notes.

The council's needs: 1. The source gives 80 L/min or more. 2. The pipe does not cross the 2019 landslide scar or the fault, where landslides and earthquakes can break it.

Table 3. Water line options
Option	Source	Flow (L/min)	Pipe route
A	Rebuild line from S1	120	Crosses the landslide scar
B	New line from S2	96	Along a gentle ridge
C	New line from S3	8	Along a gentle ridge
D	New line from S4	60	Crosses the fault
E	S3 and S4 together	68	Crosses the fault

11.

Which option meets both of the council's needs?

A. Option A
B. Option E
C. Option B
D. Option D

12.

In the next valley to the north, the same sandstone sits on the same shale at about 1,450 m. There, the layers tilt down toward the valley on its east side and away from it on its west side. Where should the team expect the strongest springs?

A. On the west side, near the river, below the bottom of the shale
B. On the east side, at about 1,450 m, where the sandstone meets the shale
C. On the west side, at about 1,450 m, where the sandstone meets the shale
D. On both ridge tops, high in the sandstone above 1,450 m

13.

Write a note to the town council explaining why the farm and the new water source must go in particular places, not just where land is cheapest. Make a claim, use evidence from at least two tables, and explain your reasoning with the geologic processes that put the soil and water where they are.