Directions: Read the question, passage, or figure carefully, and choose the best answer.
Tourists flock to Yellowstone National Park each year to view the geysers that bubble and erupt throughout it. What most of these tourists do not know is that these geysers are formed by a caldera, a hot crater in the earth’s crust that was created by a series of three eruptions from an ancient supervolcano. These eruptions, which began 2.1 million years ago, spewed between 1,000 and 2,450 cubic kilometers of volcanic matter at such a rate that the volcano’s magma chamber collapsed, creating the craters.
1. Which of the following is the topic of the passage?