Arnold Ice Cave is a well-known lava tube segment (from which the system name was derived) entered at the southeast wall of a collapse pit. Descent into the tube is quite steep (up to 30°) and much of the passage floor is covered with thick ice sheets. Uncollapsed lava tube length is less than 75 meters; the last 10 meters is somewhat more level, although the ceiling trends downslope 16° to meet the ice-blocked passage. Original lava tube walls and ceiling are preserved only near the end in a small cupola. Three distinct flow lines are visible on the southern wall, the remainder of the tube is marked by wall and ceiling spallation. High porosity and poor conductivity of basalt make it an excellent natural insulating material which, in combination with the roof thickness (about 30 m near the terminus) and orientation of the tube entrance with respect to the sun, results in preservation of ice throughout the year. Early settlers in the Bend area visited Arnold Ice Cave to obtain ice, and at one time the ice was commercially mined. Deschutes National Forest designated the site as the Arnold Geological Area and has constructed a parking facility, pathway, and wooden stairway over the ice slope into the lava tube.
The Arnold Lava Tube System (or Arnold system) is series of lava tubes within Deschutes County, Oregon, of the United States. It is located several miles southeast of the city of Bend. The system starts within the Deschutes National Forest on the northern flank of Newberry Volcano, heads northeast onto BLM land before finally terminating on private property near Horse Ridge. The system acted as a conduit for the lavas from Lava Top Butte that later fed the Badlands rootless shield. The lava flow that created the Arnold system is also referred to as the Basalt of the Badlands and is related to the Badlands Excursion which is a lava flow that created the Horse Lava Tube System. The lavas of Lava Top Butte, the Badlands, the Horse system, and the Arnold system all have a geologic age of around 80,000 years old.
The system got its name from Ronald Greeley of NASA who named it during his study of lava tubes for the Oregon Department of Geology and Mineral Industries. He based it on one of the first discoveries in the system: Arnold Ice Cave. The cave was discovered by Americans as early as 1889 and referred to as the Crook County Ice Caves. Arnold Ice Cave was also the site of an early ice mining operation. The ice was sold to the city of Bend and relieved the ice market which was cornered by one of the early saloon keepers. At one time, a trench was chopped into the ice by Jim Anderson and Phil Coyner in the 1950's. They gained access to about a half mile of passage. Years later, after the ice mining had ceased, the cave filled back up with ice, and the inner passages within the cave proved to be inaccessible to exploration attempts. Many years later, in the early 1970's, Ronald Greeley, during his research on lava tubes, named one of the caves in the system. Deg Cave was named after the initials of Donald E. Gault, the Branch Chief for Planetology at NASA Ames Research Center.
Though Americans lay claim to the discovery of the caves, they had been known long before to native Americans and as early as 1370 AD. This was determined from carbon dating nearby Charcoal Cave no. 1.