USING MAAR-DIATREME GEOMETRIES TO CONSTRAIN SUBSURFACE INFLUENCE ON EXPLOSIVE MAGMA WATER INTERACTIONS

Maar-diatreme volcanoes differ from other small volcanoes as a large proportion of the deposits are located in the subsurface in a downward tapering diatreme. The diatreme records evidence of explosive interactions between rising magma and ground water/ice. The diatreme is key to reconstructing the depth and conditions of the water that contributed to phreatomagmatic explosions. Satellite imagery has allowed more exhaustive studies of what a typical intact maar crater looks like (n>450), but similar studies of diatremes must rely on field studies of eroded diatremes and rare geophysical studies.

This study reviews published diatreme geometries leveraging different compositions, ages, and level of erosion to establish the range of common diatreme shapes and depths. Preliminary trends (n=34) reflect a wide range of diatreme geometries. Maar-diatremes can reach depths >1500 m approaching that of kimberlite diatremes >2000 m, but many examples <600 m are common. Many diatremes are steep at great depth (60-90 degrees), but wall angles of <50 degrees can occur at depths <500 m. Although diatreme widths narrow with depth, several examples are >200 m at depths of 1500 m. Regardless of wall slope angle, diatreme diameters are consistently smaller than observed crater diameters.

Maar craters commonly demonstrate multiple overlapping circular components reflecting lateral relocation of explosions during the eruption and diatremes have been shown to have multiple downward tapering bodies up to 500 m depth. These diatreme trends in angle, complexity, and diameter, suggest that lateral explosion migration occurs predominantly at shallower depths <500 m. Expansion of this catalog leveraging additional published geophysics, bore hole, and field observations would help constrain common trends in diatreme geometry and external influences such as host rock type, magma composition, and hydrology. Diatreme characterization is a necessary step to prepare for future maar-diatreme eruptions by identifying what aspects of the subsurface geology and hydrology should be characterized and monitored prior to future eruptions. Finally, constraining the depths of diatremes has implications for paleoclimates on Earth and Mars.