Hole in the Ground is a spectacular bowl-shaped volcanic crater located on the western edge of the Fort Rock Basin and at the southern margin of lavas from Newberry Volcano. It is located two miles off Oregon Highway 31, twenty-four miles southeast of La Pine and eight miles west northwest of Fort Rock in the northwest corner of Lake County. Because of its unique circular shape and depth, it was originally believed to be a meteorite impact crater.

In 1961, geologists Norm Peterson and Ed Groh published the first paper on Hole in the Ground, describing its volcanic origin. Later geologist Volker Lorenz concluded that the crater originated from a series of four major explosive events as basaltic magma rose and came into contact with abundant ground water at 1,000 to 1,600 feet below the surface. His study confirmed that Hole in the Ground was a maar (a shallow crater made by explosive eruptions) formed as a result of hydro volcanism. Following the initial explosion, occasional collapse of the overly steep vent walls into the crater intermittently closed the vent. Then changes in the ground water supply and the accumulation of pressure below the crater led to the next vent-clearing explosion. Lorenz estimated that the eruption lasted a few days to a few weeks.

Lorenz suggested that the eruption occurred between 13,500 and 18,000 years ago, which is consistent with a high water level of now-dry Fort Rock Lake, one of several large lakes in central and eastern Oregon associated with the Pleistocene, the last major glacial epoch. Fort Rock Lake was a prehistoric lake, and Hole in the Ground was above the lake level and would not have been eroded by the lake water. A high lake level and, therefore, a high ground water level was necessary for the maar eruption to occur, so the eruption could have occurred during a glacial period. More recent studies indicate an older age, perhaps coinciding with an earlier glacial epoch, as indicated by the lava flows that lap against the crater rim-forming explosion deposits and have an age between 50,000 and 100,000 years. In maximum dimension, the crater is a mile across, with a depth of over 500 feet.

Hole in the Ground is just one of many hydrovolcanic features in the extended Fort Rock Basin, including the larger, more complicated, but mostly hidden Big Hole located six miles to the west. It is approximately 6000 ft across and 300 feet deep. Both features are well worth a visit for those curious about unique volcanic features in Central Oregon.

Contributed by Steve Lent, Historian