HR: 09:45h
AN: V51B-08    [PDF]
TI: Numerical Simulations of Volcanic Eruptions Through a Crater Lake
AU: * Morrissey, M
EM: mmorriss@mines.edu
AF: Colorado School Mines, Dept. of Geology 1500 Illinois St, Golden, CO 80401 United States
AU: Gisler, G
EM: grg@lanl.gov
AF: Los Alamos National Laboratory, X-2, MS-T087, Los Alamos, NM 87545 United States
AU: Gittings, M
EM: gittings@lanl.gov
AF: Los Alamos National Laboratory, X-2, MS-T087, Los Alamos, NM 87545 United States
AB: Results are presented from a series of numerical simulations of a layered column of magmatic fluids instantaneously released through a crater lake and into the atmosphere. The simulations are calculated from the adaptive mesh refinement two-dimensional multi-material hydrodynamic computer code SAGE (Simple Adaptive Grid Eularian) developed at Los Alamos National Laboratory. The computational domain includes a conduit connected to a crater that is filled with water and atmosphere. The walls are either rigid or have a finite strength defined by the rigidity. The geometry of the conduit, crater (inner and outer walls) are scaled according to the parameters estimated for Mt. Ruapehu volcano, N.Z. The crater lake is 480 m wide, 138 m deep with a base width of 50 m that corresponds to the width of the conduit. The lake temperature is 40-60C. The conduit is layered with an upper steam rich layer at 750C this is underlain by andesitic magma at 950C. The thickness of the steam rich layer varies from 10m to 200m and the pressure inside the conduit ranges from 0.5-5.0 MPa. The fluids inside the conduit are release instantaneously into the crater lake. The following sequence of events is observed during the release of the pressurized steam-rich layer on a time scale on the order of 10s of seconds: a pressure wave is released into the water and propagates through the lake and into the atmosphere and causes a series of complex reflections in the lake. As magmatic fluid flows out of the conduit into the lake, the lake level rises to accommodate the expanding fluid. The amount that the lake level rises depends on the volume and pressure of the upper gas rich layer. We show that at a pressure of at least 1.0 MPa and a volumetric ratio of lake water to magmatic gas of less than 1.1 are required to raise the lake level on the order of 1-10s meters. Such water levels may allow water to drain down the outer crater walls. The water level begins to drop once the expanding fluid looses sufficient heat to the lake water. Lake water that was pushed up along the inner crater walls begins to drain back down and into the conduit. The downward motion of the lake water and upward movement of steam collide to generate a pressure wave in the atmosphere. This sequence of events though generated from a simple eruption scenario, may be one of the mechanisms for lahar generation (Mt. Ruapehu volcano, N.Z.), updoming of the sea or lake surface prior to eruptions (Ritter Island, Papua N.G., Mt. Ruapehu volcano, N.Z.), and rapid evaporation of crater lakes observed during crater lake eruptions (Mt. Spurr, Alaska). The sequence of event becomes more complex when the walls deform, magma rises through the crater and a thermal source is used to pressurize the conduit prior to eruption. All results will be presented in a series of parametric animations.
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting