Basalt, Buttes and Channeled Scablands
Key to Mile Markers and Highways Notation
[1.3 MM 282 US 2]
(Description of point of interest)
|Trip Mileage||Mile Marker||Highway|
|1.3||MM 282||US 2|
[0.0 MM 277 I-90]
The trip begins at Exit 277 on Interstate 90 where US Highway 2 heads west. Set your trip odometer to 00.0 as you go under the exit sign. The trip mileage and nearest mile markers (MM) are given as a reference but may not exactly match your vehicle odometer.
|"Like most people while traveling I usually pay attention to road signs, traffic and objects within a few feet of the road rather than looking closely at the passing landforms. In the process of taking the photographs for the trip I was amazed at all the geological features that I never knew were there. Next time you are on a road trip, drive a little slower so you can appreciate the wonders of nature that surround you." [Draggoo]|
[1.3 MM 282 US 2]
As we travel the first mile we see colonnades of Columbia Plateau basalt in the road cuts. The peculiar columns are caused by crystallization of the molten lava as it cools and shrinks forming 5 to 7 sided columns. The columns are from 12 to 30 inches across.
Our moon has large dark areas of basalt lava called "mares", Latin for seas. The early astronomers thought there might be oceans on the face of the moon. Mars has lava flows as well. In the NASA/JPL image at right the light and dark layers of a flow can be seen. It is part of a much larger area. Click on image for a detail view.
This is the NASA description of the full image:
"The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 1998 confirmed that a vast region of Mars south of the Elysium volcanoes is covered by a relatively young lava surface that was very fluid when it erupted--so fluid that it ran more than a thousand kilometers (more than 600 miles) across a region known as the Elysium Basin and a channel named Marte Vallis."
"When it was forming, the lava flowed from the lower left, toward the center right, then curved to the left and flowed toward the top-center of the frame. The center of the lava flow in image 38804 has a wide, shallow channel bounded by steep, discontinuous walls--also known as levees. Such leveed channels are commonly the conduit through which some of the later stages of molten rock are transported along a lava flow. The margins of the lava flow are broken into plates--some of them several kilometers across. These plates were once part of a hard, rock crust that floated on molten lava. As the lava flowed down Marte Vallis, huge chunks of this crust broke off at the margins of the flow and floated a few kilometers away from where they had originated. Long after the lava had cooled and hardened, a distant meteorite impact splashed ejecta across the martian surface such that a field of small craters--known as secondary craters--formed on top of the lava flow shown here."
[2.0 MM 281]
Looking north, we see ancient volcanoes, intrusives, and glacial sediments that formed mountain peaks. Intrusives are where magma flows don't break through the surface but do raise the ground above them. These mountains were at the southern edges of the glaciers of the last ice age, about 10,000 years ago.
Columbia Plateau Basalt
The material in basalt is from molten rock, called magma, deep within the Earth's crust. Fully melted rock in magma that reaches the surface cools into granite. When the magma is from partially melted rock the lava becomes basalt. The Columbia Plateau Basalt formed about 10 to 30 million years ago.
Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Volcanic rock caused by partial melting of the Earth's crust.
- Current Ripple
- Mark left on streambed from water current usually less than an inch high and a few inches between the tops (crests) of each ripple. The giant ripples from Lake Missoula floods are as much as 35 feet high and several hundred feet between. See also Ripple Mark.
- Places where magma flows don't break through the surface but do raise the ground above them.
- Molten earth material (rock) that comes out of volcanoes or cracks in the Earth's crust.
- Molten rock beneath the earth's surface. Magma is called "lava" when it erupts from a volcano.
- Pale yellow, glassy material that forms when hot steam and other gases contact water during a lava flow. Sand and clay is usually mixed in as well.
- Pillow Basalt
- Basalt formed underwater or as a basalt flow contacts a river or lake.
- Ripple Mark
- See also Current Ripple. Parallel, elongated mounds of sediment formed in wind or water currents. Large ripple marks found in the Channeled Scablands were the most convincing evidence for the Missoula Floods. See also Glacial Lake Missoula.
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