HR: 0800h
AN: V31E-0715    [Abstracts]
TI: STUDY NEW PREGRESS ON VOLCANIC PHREATOMAGMATIC ERUPTION
AU: Sun, Q
EM: qiansunstr@sina.com
AF: Institute of Geology, China Earthquake, Institute of Geology, China Earthquake Administration, P.O.Box 9803£¬Beijing, China, Beijing, 100029, China
AU: * Fan, Q
EM: fqc@ies.ac.cn
AF: Institute of Geology, China Earthquake, Institute of Geology, China Earthquake Administration, P.O.Box 9803£¬Beijing, China, Beijing, 100029, China
AU: Li, N
EM: lini67@sina.com
AF: Institute of Geology, China Earthquake, Institute of Geology, China Earthquake Administration, P.O.Box 9803£¬Beijing, China, Beijing, 100029, China
AB: As an essential and important type of volcanic eruption on earth, phreatomagmatic eruption is characterized by groundwater-related explosive eruption and subsequent base surge deposit and maar lakes. Base surge deposit and maar lakes are widely distributed all over the world, and also in the Northeast China and the southern China. Study of phreatomagmatic eruption maybe dated back to 1921, and in the following over 80 years, many works have been done on phreatomagmatic eruption, using various of methods of volcanic geology, petrology, sedimentology, physical volcanology and digital modeling, to discuss its origin and mechanism. In this paper, we focus on the geological feature of the base surge deposit and dynamic mechanism of the phreatomagmatic eruption. When ascending basaltic magma meets with ground ( surface ) water, violent explosion would occur, this action was called phreatomagmatic eruption. The main product of this kind of eruption are maars and base surge. As to the base surge, it has long been treated as sedimentary tuff by mistake. Usually, base surge is distributed around maar, different from the distribution of sedimentary tuff. Typical phenomena of base surge caused by phreatomagmatic eruption can be observed through the detail field work, such as large-scale and low-angle cross-bedding, slaty-bedding, current-bedding and distal facies accretionary lapilli. In order to explain the dynamic mechanism of phreatomagmatic eruption thoroughly, we propose a simple model in this paper in light of the elasticity theory. Some conclusions can be drawn as follows: the larger the radius of maar, the larger the explosive wallop needed for the formation of maar is; provided that the radius of maar and depth of explosive point are limited, then the larger the area of contact surface between magma and groundwater, the stronger the explosive energy will be; if the explosive energy and area of explosive point are restricted, the larger the radius of maar, the greater the depth of explosive point can be inferred; when the explosive energy and radius of maar are qualified, the depth of explosive point decreases with increasing of the area of contact surface between magma and groundwater. As for the maximum stress, undoubtedly it should occur on the surface of the overlying formation.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 3610 Geochemical modeling (1009, 8410)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting