Basalt with dunite nodules, Western Victoria, Australia

To learn more about how geoscientists classify the variations in volcanic and other igneous rocks, read the blog article A Million Names.

In 2018, all eyes are on the erupting volcanic magmas of Hawaii – rivers, fountains, and vertical plumes – all producing a dark, fine-grained rock known as basalt. Basalts melt in the earth’s mantle and are relatively low in silica – hence they are ‘runny’ or have low viscosity.

Continued eruption at Fissure 8 feeds the voluminous lava channel to the ocean as seen during an overflight of the lava-flow field.

Grant County
Oregon, United States

Flood basalts are giant eruptions of basalt that have covered very large areas in basalt. The Columbia River Basin has over 164,000 square kilometers of flood basalt inundating many states (NV, CA, ID, OR, and WA). This is thought to have occurred due to a subducting plate underneath Oregon  ~17 million years ago, and is thought to be the beginnings of Yellowstone volcanism. Grant County is specifically known for its basaltic dikes and igneous silicic rocks of granite and gabbro.


Thayer, T. P., Case, J. E., & Stotelmeyer, R. B. (1981). Mineral resources of the Strawberry Mountain Wilderness and adjacent areas, Grant County, Oregon.  Geological Survey Bull 1498.

Liu, L. & Stegman, D. R. (2012). Origin of Columbia River flood basalt controlled by propagating rupture of the Farallon slab. Nature 482, 386–389.

Grant County, Oregon

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