Figure 8. Generalized cross-section, Copper River Basin, showing position of overpressured compartment and mud volcano; fluidized rock material, mainly shale, and high-pressured water with minor hydrocarbons from the overpressured compartment are being ejected and vented at the surface to form a mud volcano. The rising, high-pressured mixture may pressure-up any shallow, permeable beds encountered, thereby locally complicating recognition of the layered arrangement of hydraulic systems.