Isachsen's quest began with a simple observation. He spreads a map out on the hood of his truck— a satellite image of New York State. "I first noticed this in the early 1970s," he says. "I had a grant from NASA to study features on this image. See all these squiggly lines? These are valleys formed by streams. That's what you'd expect a valley to look like. All squiggly, going in no particular direction. Now here's where we are. That's the valley formed by the Esopus Creek and its tributary, Woodland Creek. It forms an almost perfect circle around Panther Mountain. So I asked myself, what on Earth would account for that?"
Isachsen had a hunch that a meteorite had plunged into the site aeons ago; the circle might be a trace of the buried crater's rim. Although a few sites of such impacts were known in those days, most crater structures were presumed to have been formed by volcanic activity. Indeed, geologists once doubted that more than a handful of meteorites had ever reached Earth. What's more, they assumed that the sheer amount of geologic activity on Earth— everything from volcanoes to plate tectonics to the simple erosive forces of wind and water— would have wiped away any traces of impacts. In the early 1970s, however, images from the Apollo missions and other planetary probes had begun to put a new face on the geology of Earth and its near neighbors. Geologists were discovering that impact craters caused by asteroids, meteorites, and other forms of cosmic debris are the most common geologic features of the planets and their moons. Earth, they realized, would not have been spared.
Closely spaced fractures in the bed of the Esopus Creek (left) in upstate New York helped feed Yngvar Isachsen's suspicion that a buried impact crater lay beneath Panther Mountain. He first grew curious about the site back in the 1970s when he noticed the creek's circular path on a satellite image (right). Such gloriously expansive views, Isachsen adds, have transformed the field of geology-and one of the results is a new understanding of the importance of impact craters to planetary geology. Isachsen has recently proven that the circular creek does indeed follow the rim of a buried impact crater.Photos by (left) Yngvar Isachsen; (right) landsat/Nasa
Isachsen initially lacked the resources to prove his hunch, but the notion that he might have a crater by the tail stirred his blood. Findings over the next few decades only strengthened his suspicion. "The science of impact craters is the new geology," says Isachsen. "We're finally realizing how important they are."
