ACT Science Practice Test 107

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


A pluvial lake is an ancient lake with high water levels, generally associated with times of high precipitation. Lake Bonneville was a prehistoric pluvial lake that covered much of North America's Great Basin region during the last ice age (see Figure 1). Most of the territory it covered was in present-day Utah, though parts of the lake extended into present-day Idaho and Nevada. Formed about 32,000 years ago, it existed until about 16,800 years ago, when most of the contents of the lake were released through the Red Rock Pass in Idaho.

Figure 1

At more than 1,000 feet (305 m) deep and more than 19,691 square miles (50,999.5 km2) in area, Lake Bonneville was nearly as large as Lake Michigan and significantly deeper. Over time, increasing temperatures in North America caused the lake to begin drying up, leaving Great Salt Lake, Utah Lake, Sevier Lake, Rush Lake, and Little Salt Lake as remnants. While each of these lakes is considered a freshwater lake, the salinity levels are higher than normal. Figure 2 shows a cross-section of part of Utah Lake and its sediment and bedrock, with measurements taken at the cities of Genola and Provo and two test sites in between.

Figure 2

1. According to Figure 2, the lake clay deposit is thinnest at which of the following locations?

A. Genola
B. Test Site 1
C. Test Site 2
D. Provo

2. According to the passage, Lake Bonneville existed in its entirety for approximately how many years?

F. 32,000
G. 16,800
H. 15,200
J. Cannot be determined from the given information

3. According to Figure 2, as the thickness of the lake clay increases from Genola to Site 2, the thickness of the bedrock beneath it:

A. increases overall.
B. remains the same.
C. first increases and then decreases.
D. decreases overall.

4. According to Figure 2, which of the following graphs best represents the elevations, in meters above sea level, of the top of the lake clay layer at Test Sites 1 and 2?


5. Great Salt Lake is fed mainly by 3 tributary rivers that deposit large amounts of minerals into its waters. The lake is salty because it has no outflow for water other than evaporation, which is predominately mineralfree. If local temperatures were to decrease significantly, while freshwater rain were to increase significantly, what would be the likely resulting change in the salinity of Great Salt Lake?

A. Salinity would decrease.
B. Salinity would increase.
C. Salinity would remain the same.
D. Salinity cannot be predicted.