Passage II
Lake Agassiz existed between 11,700 and 9,500 years ago in North America (see Figure 1). The lake was formed when a large glacier dammed several rivers. Groundwater trapped in lake and glacial sediments provides information about the climate at the time the sediments were deposited. Figure 2 shows a cross section of the sediments (lake clay and glacial till) and bedrock in the area. Figure 3 shows the δ18O values of groundwater taken from samples of the top 40 m of sediment at 3 sites along the same cross section. δ18O is calculated from a ratio of 2 oxygen isotopes (18O and 16O) in the groundwater. Smaller δ18O values indicate cooler average temperatures.
9. According to Figure 2, which of the following graphs best represents the elevations, in m above sea level, of the top of the glacial till layer at Sites 1, 2, and 3 ?
Your Answer is
Correct Answer is C
Explanation
Look at figure 2, the altitude of the glacial till is the highest at Site 2, and the altitude of the glacial till is the lowest at Site 3