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The Badlands near Bend, OR, have unique geologic interest for the hiker

Geology of Badlands Wilderness Study Area
By Larry Chitwood
Deschutes National Forest
16 Feb 2005

The Badlands Wilderness Study Area holds a number of remarkable and exciting landforms and geologic features. Most of the study area includes the rugged Badlands volcano, which has premiere features of inflated lava. Windblown volcanic ash and eroded lava make up the sandy, light-colored soil that covers the low and flat places in these fields of lava. Dry River, active during each of several ice ages, marks the southeast boundary between two volcanic areas – Badlands volcano and the Horse Ridge volcanoes. Earth movements along the Brothers Fault Zone have faulted and sliced up the old Horse Ridge volcanoes, but not Badlands volcano.

Lava of the Badlands came from Newberry Volcano to the southwest. Eruptions took place near Lava Top cinder cone about 80,000 years ago. A USGS geologist in 2004 named this lava flow the Basalt of the Badlands. The eruptions probably ac-companied catastrophic explosive eruptions at the top of Newberry Volcano, which formed Newberry Caldera (also called Newberry Crater).

The Badlands formed in an unusual way. The flow that supplied lava to the Badlands apparently developed a hole in the roof of its main lava tube. This hole became the source of lava that built a shield volcano that we call the Badlands (technically, a rootless shield volcano). An irregularly-shaped pit crater at the top of the shield marks the site where lava flowed in all directions to create the Badlands. It’s located about 1500 feet northeast of milepost 15 on Highway 20. Highway 20 traverses the shield along a straight, five-mile stretch between the inter-sections with an old section of Highway 20 (between mileposts 12.6 and 17.5).

The Badlands are rough and highly irregular. Piles and ridges of angular basaltic boulders full of holes and cavities project chaotically out of the ground. Large slabs of lava tilt at every angle. Is-lands of lava with flat or ridge-like tops project above the chaos and offer fine views. The tallest of these is 100-foot-high Badlands Rock. To the immediate west are the island-plateaus of The Castle and Flat-iron, with great sand-filled moats and cracks encircling their nearly flat, elevated tops.

Nearly everywhere are low places a few feet to tens of feet deep, depressions with floors of soft sandy soil. Some low places are nearly circular, but most are irregular and connect with a string of depressions. Cracked sheets of lava tilt steeply inward. In places among the tilted sheets, small flat-floored caves offer relief from wind and rain.
These descriptions are characteristic of inflated lava. The knowledge and vocabulary of inflated lava is still relatively new, dating to the 1980s. The surface of inflated lava can indeed seem chaotic, but many of the processes and features are now well-known and understood.

For lava to inflate and create characteristic land-forms, it must be quite fluid and it must be erupted onto land with a gentle slope or no slope. Basaltic lava and the nearly flat landscapes west of Horse Ridge fit the bill.

Imagine lava erupting onto a dry, flat lakebed (which is what happened at the Diamond Craters lava field near the Malheur National Wildlife Refuge). The lava spreads out in all directions, like pouring pancake batter on a griddle. At first the spreading edge moves fast, but as time goes by the spreading edge moves slower and slower. At some point, the lava moves so slowly that it freezes and stops moving. Meanwhile, the top of the lava sheet has been cooling to form a thickening, hard crust. You can walk on it, but your boots will probably smoke.

Even though the edge has stopped moving, lava is still erupting and flowing into the interior of the sheet. At this point the lava sheet begins to swell up or inflate, and the surface begins to rise. The lava sheet can thicken from an initial ˝ to 1˝ feet thick to tens of feet thick. A fully developed lava sheet with its elevated flat top is called a pressure plateau. If you walk around the upper edge of a pressure plateau, you will see steeply tilted slabs of lava crust called rotated or tilted crust. With time as lava continues to pour into the sheet’s interior, it begins to leak and form lobes where the process begins again.

Let’s back up. Imagine what would happen if the spreading lava sheet encounters a small, two-foot-high hill. The thin lava flow would surround the hill but not cover it. Later when the lava sheet inflates, the small hill becomes the floor of a pit or depression, which may be 20 or more feet deep. Encounters with a small circular hill would result in a deep circular pit called a plateau pit. Encounters with an irregularly shaped hill would result in a residual depression.

If a long finger of lava spreads over the land and inflates, the crust that forms over the finger usually cracks down the middle. Slowly, the two sides of the crust are pushed up and tilted outward forming an inflation crack. If you were watching the developing crack, you would see a molten, red-hot line at the bottom, but the process is too slow to see movement. Cracks like these form around the upper edges of pressure plateaus and account for the impressive soil-filled moats at The Castle and Flatiron.

Normally, long fingers of lava inflate much more at their wider sections creating swollen or tumescent areas with cracks down their middle. These are called tumuli and, along with their highly elongated cousins called pressure ridges, are common in the Badlands. Badlands Rock is an excellent, but giant, example of a tumulus (tumuli, singular; tumulus, plural). Its great size may well place it in the world’s top ten of giant tumuli.

Numerous caves can be found in the Badlands including lava tubes and lift up caves. But they’re small and you can’t usually stand up in them. Molten lava drained from the interior of hardened channels to form lava tubes. Lift-up caves may form when inflating lava carries a tilted slab of lava upward. A horizontal crack opens near the base of the tilted slab big enough for a person to each lunch and not get wet in a rainstorm.

Since the Badlands lava is relatively young and only slightly eroded, it’s not completely buried in soil. About half the soil is an old mixture of wind-blown volcanic ash and of sandy, eroded pieces of lava. The newer, upper half is Mazama ash, the volcanic ash from the great eruption of Mount Mazama (Crater Lake) 7700 years ago. If all the soil were evenly spread, it would be about two feet thick. Wind, frost heaving, and local surface water have carried nearly all soil to the closest low areas. During the last ice age (the Wisconsin), which peaked about 20,000 years ago, a pine forest probably grew in the Badlands and surrounding area during the colder and wetter climate.

Harsh conditions during the last ice age accelerated a curious form of erosion in the Badlands. The surface of some lava slowly eroded into smoothly sculpted pockets and holes, a process called cavernous weathering. Birds can nest in the small holes and children can play hide-and-seek in the large ones. The shapes of these weathered surfaces can look very attractive, as if an artist had created modern rock art. To make these holes and pockets, the lava must be porous. Indeed, a microscopic network of tiny interconnected cavities allows rainwater to saturate the interior of the lava. During the deep freeze conditions of the last ice age, the tiny water-filled cavities at the surface would repeatedly freeze and pop off sand-size pieces of lava a few at a time. The rate of erosion is greatly reduced in today’s warmer and dryer climate.

The nearby 300-foot-deep Dry River Canyon dramatically records evidence of an impressive river that once cascaded down through its depths. Water cut the canyon and left a fan of sand and gravel below the canyon, which has been used to construct and maintain nearby Highway 20. Only during ice ages does a river flow through the canyon. Below the canyon, the Badlands lava erupted between the last two ice ages so the river had to find a new path across the lava during the last ice age. In places the new channel is well defined with smooth and fluted rocks and little box canyons. In others, there is no channel, just fields of sand or tell-tale rounded gravel here and there. Hiking the path of the old river is an exciting challenge.



Read more . . .

  The Badlands Wilderness
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Deschutes County Commissioners hearing on Badlands Wilderness support
OHV use restricted in Upper Deschutes Resource Management Plan

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Vandals destroy ancient pictographs in the Badlands
Senator Wyden tests support of Badlands Wilderness
Badlands Wilderness endorsed by Bend City Commissioners
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The Badlands unique geologic forms explained by Chitwood  pdf
The Badlands, a brief history  
The Badlands pictographs reported 75 year ago

Map of huge exclusive OHV areas adjoining the Badlands