Hole in the Ground Maar, Oregon
Posted by: 
Volcanoguy
N 43° 24.643 W 121° 11.886
10T E 645889 N 4808002
Hole in the Ground is nearly a mile in diameter, as much as 500 feet deep, and is the result of the interaction of rising magma and meeting abundant groundwater.
Waymark Code: WM1NRD
Location: Oregon, United States
Date Posted: 06/10/2007
Views: 146
Hole in the Ground is a volcanic explosion crater or maar located on the west edge of the Fort Rock basin. The term maar comes from the Maar Lakes of Germany which occupy a group of these explosion craters.
Hole in the Ground is approximately 4500 feet east-west by 5500 feet north-south. The floor of the crater is at an elevation of 4340 feet, while the surrounding area has an elevation of about 4650 feet. The rim ranges in elevation from 4690 to 4855 feet. During glacial time the Fort Rock basin was a large lake that reached a maximum elevation of 4540 feet with other prominent lower lake stands such as 4430 feet.
The eruption which formed Hole in the Ground has not been dated but likely occurred during during glacial period when Fort Rock Lake was in existence less than three miles to the east.
The eruption probably lasted a few days or weeks and consisted of a series of explosions due to rising basaltic magma coming into contact with abundant ground water at depth. The magma may have been rising along the fault which is exposed in the crater walls. The layering visible in the rim records the pulsing of the eruption resulting from repeated slumping and subsidence of the crater walls, changes is the supply of ground water, and repeated pressure buildup.
Here’s a link to some photos of Ukinrek Maars in Alaska which formed in 1977. (
visit link)
There are three access points to the rim and a primitive road circles the rim.
Access Points:
East N 43° 24.558 W 121° 11.314
North N 43° 24.948 W 121° 11.435
West N 43° 24.754 W 121° 12.321