MAGMA-SEDIMENT INTERACTIONS: MODELING THERMAL AND STEAM GENERATION EFFECTS OF BASALTIC MELT CONTACT WITH WET AND DRY SEDIMENTS USING LARGE-SCALE EXPERIMENTAL CONSTRAINTS

Magma or lava contact with sediment is a very common phenomenon. Melt-sediment contact drives multiple processes, including creating sediment alteration zones, generating and transporting steam, producing melt-sediment interaction structures, and governing magma-water interactions. Better understanding of these processes furthers our knowledge of volcanic eruptions, volcanic driven geothermal systems, assessing buried infrastructure hazard risks, and inferring melt emplacement conditions from the geologic record. However, the melt, water, and sediment conditions required for these processes are still poorly constrained.

We use experimental data from nine meter-scale experiments emplacing ~50 kg of remelted basaltic material in a 5-11.5 cm melt layer over 18 cm of sediment. Sediments include well-sorted sand, moderately sorted sand, sandy gravel, gravel, bomb and lapilli scoria, and pumice lapilli. Melt temperatures vary from 1275°C to >1350°C, and sediment water content ranges from dry (<5%) to saturated (40+%) by pore space volume. Thermocouples are located every few cm from the melt contact to the sediment base, and a FLIR infrared camera tracks surface temperature.

We use COMSOL multiphysics to model the experimental system. We include melt radiative losses, and heat transfer to the sediment as a porous, water-bearing media. The melt properties are temperature dependent, and we model the phase change of water to steam, and the migration of water and steam away from the melt. Model results are compared to the time-dependent thermocouple and FLIR data, and can be closely matched. The total available amount of heat from the melt —governed by melt thickness and initial temperature—strongly affects resulting sediment temperatures. In addition, the amount of pore space water, the phase change to steam, and the permeability of the sediment (and ease of water and steam migration) are major factors in peak sediment temperatures, and govern whether the steam migrates away from the melt, or through the melt, generating more dynamic melt-water interactions.