Implications of magma transfer between multiple reservoirs on eruption cycling.

Volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate. We used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the Soufrière Hills volcano on Montserrat, West Indies. For three cycles of effusion followed by discrete pauses, supply of the system from the deep crust and mantle was continuous. During periods of reinitiated high surface efflux, magma rose quickly and synchronously from a deflating mid-crustal reservoir (at about 12 kilometers) augmented from depth. During repose, the lower reservoir refilled from the deep supply, with only minor discharge transiting the upper chamber to surface. These observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid-crustal reservoir, episodically valved below a shallow reservoir (at about 6 kilometers).

Computer - simulation models of pyroclastic flows and lahars at Soufrière hills volcano, Monserrat : Applications to hazard assessment

Soufriere hills Volcano (Monserrat, British West Indies) consists of a series of andesitic lava domes, English's Crater, a horseshoe-shaped depression opening to the east - northeast, contains the youngest dome prior to the onset of volcanic activity on 18 July 1995 and the creation of the 1995-1996 dome complex. The computer code FLOW3D is being used to simulate several types of volcanic flows that have been observed or may potentially occur at soufriere Hills. Because of their predominance at Soufriere Hills, an understanding of pyroclastic flows produced by the disintegration of lava domes is critical . In this study, we concentrated primarily upon pyroclastic flows and lahars, as well as examine an energy - cone model. The programs first constructs a digital terrain model based upon a 3-D network of (x,y,z triplets. The triangulated irregular network (TIN) of digitized topographic data serves as the basic for the numerical computations. Gravitational acceleration and flow retardation are iteratively calculated for each flow elements as it passes over the finite element net. The shear stress retarding the flows is divided into three parameters: basal friction, internal viscosity (or viscous drag), and inertial acceleration (or dissipation). Estimated values and limits for these flow parameters are based upon the know distribution of products from Soufriere Hills and the observations of actual flow of various types at other volcanoes. Any desired number of flow paths can be traced to their terminations with the velocity displayed on a color scale. An animated eruption image is presented on a computer screen as a three - dimensional model. These computer simulations ca be exptremely useful in assessing and mitigation the risk associated with several types of volcanic hazards. (AU)