It wasn't until his later years, in the early 1990s, that Isachsen was able to devote more time to the crater question. Since the walls of a newly formed impact crater are often unable to support themselves, landslides occur and build up a mound of rock and soil in the center. This results in a lower density of rock and thus slightly reduced gravitational pull, which can be measured. Isachsen took a gravimeter along on two hikes up the mountain and took regular readings. As he had expected, the gravity in the area was slightly lower than other mountains of comparable elevation in the Catskills, adding more weight to the crater theory.