Four Craters Lava Field eruptions from the field were accompanied by a slight sinking of the older rock surface. This shallow, graben-like sink is about 3 kilometers wide and extends to the south into an old lake basin. Crack-in-the-Ground marks the western edge of this small, volcano-tectonic depression and is nearly 9 meters deep and over a meter wide. The crack is the result of a tension fracture along a hingeline produced by the drapping of Green Mountain lava flows over the edge of upthrown side of the concealed fault zone. Four Craters Lava Field Four Craters Lava Field is a basaltic volcanic field
Lava Creek Tuff tuff layer is approximately . Lava Creek Tuff The Lava Creek Tuff is a tuff formation in Wyoming, Montana and Idaho, United States, created during the Lava Creek eruption around 630,000 years ago, which formed the Yellowstone Caldera. The Lava Creek Tuff is distributed in a radial pattern around the caldera and is formed of of ignimbrites. The tuff has been exposed by erosion at Tuff Cliff along the Gibbon River. Lava Creek Tuff ranges in color from light gray to pale red in some locales. Rock texture of the tuff ranges from fine-grained to aphanitic and is densely welded.