The Lava River Cave near Bend, Oregon, is part of the Newberry National Volcanic Monument, which is managed by the United States Forest Service. The cave is an excellent example of a lava tube. At 5,211 feet (1,588 m) in length, the northwest section of the cave is the longest continuous lava tube in Oregon. While the cave’s discovery in 1889 was officially credited to a pioneer hunter, the presence of obsidian flakes near the cave has led archaeologists to conclude that Native Americans knew about the cave long before settlers arrived in central Oregon.
The cave's entrance appears as a large hole in the ground. At its mouth, the entrance trail drops suddenly over a jumble of volcanic rocks. This area is known as the Collapsed Corridor. It is the result of ground water freezing in rock cracks in the ceiling. Loosened rocks eventually fall. Over the centuries, the fallen rocks have accumlated into a large boulder pile. Since freezing temperatures occurs only near the mouth of the cave, most rock-falls are in this area. To get down the rock pile, visitor must descend 126 steps with guard rails for safety. At the bottom of the stairs is a large cool chamber where winter ice fills cracks in the floor and ice stalactites often cling to the ceiling until June.
After a short walk, the ceiling reaches a height of 58 feet (18 m). At this point, the width of the cave is 50 feet (15 m). This massive volcanic archway is called Echo Hall. The smooth walls are remarkably symmetrical so sounds echo in the huge chamber. In this section, remnants of the ancient lava flow’s current can be seen molded in the tunnel walls. They appear as rounded over-hanging shelves and lateral markings etched in the walls. The end of this hall is about 1,500 feet (457 m) into the cave. At that point, the cave passes under Highway 97. The underground crossing is marked by a small sign post.
Glazed walls in the cave's Low Bridge area
Beyond the Highway 97 marker, visitors enter an area called Low Bridge Lane. In this area, the ceiling drops to less than six feet (1.8 m). This section of the cave was created after most of the molten lava had drained out of the cave leaving hot gases trapped in the interior of the tube. These gases re-heated the lava tube causing the tunnel walls to re-melt. As re-melted rocks cooled, the walls were left with a shiny, glazed surface. There are also volcanic stalactites in this area of the cave. These formations are sometimes called lavacicles. They are found in two forms. Some are hollow cylindrically shaped soda straws, formed by escaping gases. The others are cone shaped drip pendants formed when re-melted lava dripped from the ceiling. At the end of Low Bridge area, the tube begins to narrow and the cave is divided into two tunnels with intermittent connecting passages. This is the Two Tube Tunnel section of the cave. Both tubes were probably active lava channels at the same time; however, the upper channel eventually drained into the lower tube as the flow subsided.
One of the most unique parts of the cave is the Sand Garden, located about 3,000 feet (914 m) from the entrance. Here the floor of the cave is covered with sand. The sand was carried into the cave by dripping water. The sand is fine volcanic ash from the eruption of Mount Mazama 6,600 years ago. Rain and melting snow carried the ash down from the surface through cracks in the rock and deposited it on the floor of the cave one grain at a time. Occasionally, enough water leaks into the cave to create a pool. This allows the sand to spread out across the floor.
At the Sand Garden, the constant dripping of water has carved spires and pinnacles in the sand. Since it takes hundreds of years to build these delicate sand forms, the Forest Service has fenced off the garden area to protect it. The 2,211 feet (674 m) of cave trail beyond the Sand Garden has a Sandy floor. Along the way, the ceiling descends lower and lower until the sand fills the cave. The last 310 feet (95 m) of the cave was dug out of the sand plug by two men in the 1930s. Exploring this section of the cave requires visitors to crawl on hands and knees for much of the distance to the cave’s end, and usually takes at least thirty minutes.