The eruptions from the Four Craters Lava Field, seen in the background, were accompanied by a slight sinking of the older rock surface, which created the Crack-in-the-Ground. It is a shallow "graben," or sinking of the earth, a tension fracture in basalt. (A larger graben in southeastern Oregon is a vertical subsidence, or sinking, of one mile of the earth from the upper to lower edge!)
The eruptions from the Four Craters Lava Field, seen in the background, were accompanied by a slight sinking of the older rock surface, which created the Crack-in-the-Ground. It is a shallow "graben," or sinking of the earth, a tension fracture in basalt. (A larger graben in southeastern Oregon is a vertical subsidence, or sinking, of one mile of the earth from the upper to lower edge!)