Tephra dispersion modeling using MM5: Example from the Cerro Negro Volcano, Nicaragua

Tephra, commonly known as volcanic ash, threatens larger areas than any other volcanic hazard. Tephra creates numerous hazards including, collapsed buildings and other infrastructure, respiratory illnesses, disruption of aviation and ground transportation, destruction of agriculture, and water contamination. Models of tephra deposition are increasingly used to assess volcanic hazards in advance of eruptions and in near-real-time. These tephra models often approximate the wind field using simplistic assumptions of the atmosphere that do not account for the four-dimensional variations in wind velocity. This study demonstrates how a well-known mesoscale atmospheric model is used to improve forecasts of the location of the major axis of dispersion for erupting plumes.

The Pennsylvania State University-National Center for Atmospheric Research (NCAR) fifth-generation Mesoscale Model (MM5) is effective at resolving mesoscale circulation patterns in areas with sparse meteorological observations and/or mountainous terrain, and thus suitable for simulating conditions surrounding the Cerro Negro volcano in Nicaragua. MM5 is used to simulate the atmospheric conditions during the 1995 eruption of Cerro Negro, Nicaragua. Estimates of diffusivity and particle settling velocities are used in conjunction with MM5-derived wind fields to forecast the plume track and tephra deposition patterns. Particle trajectories from the MM5 winds are compared with tephra accumulation maps and satellite imagery.

The particle trajectories generated from the complex MM5 wind fields closely matched the observed multi-lobed plume dispersion axes. The results demonstrate that the appropriate application of mesoscale atmospheric models should ultimately improve tephra hazard assessments, especially in the absence of abundant meteorological observations.