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
Seamount igneous intrusions, in the forms of dikes and sills, are also an important part of seamount growth. The most common type of flow is pillow lava, named so after its distinctive shape. Less common are sheet flows, which are glassy and marginal, and indicative of larger-scale flows. Volcaniclastic sedimentary rocks dominate shallow-water seamounts. They are the products of the explosive activity of seamounts that are near the water's surface, and can also form from mechanical wear of existing volcanic rock. Seamounts can form in a wide variety of tectonic settings, resulting in a very diverse structural bank. Seamounts come in