Volcanic plateau up by foundering of the Earth's crust to form the present ocean basin. The Earth features numerous subaerial and submarine volcanic plateaus such as the Columbia River Plateau (subaerial) and the vast Ontong Java Plateau (submarine). Pyroclastic plateaus are produced by massive pyroclastic flows and they are underlain by pyroclastic rocks: agglomerates, tephra, volcanic ashes cemented into tuffs, mafic or felsic. Examples include Shirasu-Daichi which covers almost all of Southern Kyūshū, Japan and the North Island Volcanic Plateau in New Zealand. Volcanic plateau A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus
Ringing rocks of symmetry. The overall geometry is cylindrical, with an average diameter of one kilometer. The pluton consists of two major units: an inner core of quartz-bearing felsic units with a diameter of 600 meters and an outer mafic unit composed of coaxial concentric layers. In map view, the complex has a bulls-eye configuration. The outer zone of the pluton consists of two alternating mafic hybrid rock types. In chemical analysis the rocks are nearly identical; however, the early stage minerals, olivine and pyroxene, were preserved in one and not the other, giving the rocks sharply different weathering properties. The rock