The effects of the host-substrate properties on maar-diatreme volcanoes: experimental evidence

Abstract

While the relationship between the host-substrate properties and the formation of maar-diatreme volcanoes have been investigated in the past, it remains poorly understood. In order to establish the effects of the qualitative host-substrate properties on crater depth, diameter, morphological features and subsurface structures, we present a comparison of four campaigns of experiments that used small chemical explosives buried in various geological media to simulate the formation of maar-diatremes. Previous results from these experiments have shown that primary variations in craters and subsurface structures are related to the scaled depth (physical depth divided by cube root of blast energy). Our study reveals that single explosions at optimal scaled depths in stronger host-materials create the largest and deepest craters with steep walls and the highest crater rims. For single explosions at deeper than optimal scaled depths, the influence of material strength is less obvious and nonlinear for crater depth, and nonexistent for crater diameter, within the range of the experiments. For secondary and tertiary blasts, there are no apparent relationships between the material properties and the crater parameters. Instead, the presence of pre-existing craters influences the crater evolution. A general weakening of the materials after successive explosions can be observed, suggesting a possible decrease in the host-substrate influence even at optimal scaled depth. The results suggest that the influence of the host-substrate properties is important only in the early stage of a maar-diatreme (neglecting post-eruptive slumping into the open crater), and decreases as explosion numbers increase. Since maar-diatremes reflect eruptive histories that involve tens to hundreds of individual explosions, the influence of initial substrate properties on initial crater processes could potentially be completely lost in a natural system.

The contribution of experimental volcanology to the study of the physics of eruptive processes, and related scaling issues: A review

“…Goto et al (2001) observed that the crater diameter (D) increased with explosion energy according to = 0.32 − 2.06, (88) and Sato and Taniguchi (1997) found that the relationship between the diameter and the volume of ejecta (V) was = 0.97 0.36 (89) and that 0.7-10% of the initial thermal energy was converted into kinetic energy. Strong host materials favored higher crater rims as well as larger and deeper craters with steep walls (Macorps et al 2016). Multiple explosions, typical of phreatomagmatic eruptions, created craters of about the same size as that of individual events of similar energy but that were narrower and deeper (Valentine et al 2012).…”

“…For a given explosion energy the optimal depth was defined as that resulting in the maximum crater diameter. With granular materials, a negligible amount of energy was consumed to fragment the host medium, unless it had some significant strength (Macorps et al 2016), in contrast to natural cases that involve coherent rocks. Experiments showed that explosions generated jets whose height was set by the normalized depth and which also controlled the distribution of ejecta from shallow levels outside (Graettinger et al 2014).…”

“…Multiple explosions, typical of phreatomagmatic eruptions, created craters of about the same size as that of individual events of similar energy but that were narrower and deeper (Valentine et al 2012). They caused progressive mixing of the crater-filling material (Graettinger et al 2014) and weakened the host medium, suggesting that material strength was important only at early stages (Macorps et al 2016). Explosions were also simulated by injecting compressed air or air-particle mixtures from a point source into a granular material.…”

How Polygenetic are Monogenetic Volcanoes: Case Studies of Some Complex Maar‐Diatreme Volcanoes

“…In soft substrates, maar-diatreme volcanoes tend to have large and bowlshaped craters, with gently dipping inner walls [91]. Recent analog experiments as well as field observations from classical diatremes cut into "soft substrate" showed that the diatreme wall can be steep for such maars that cut through soft substrate (e.g., [121][122][123][124][125]). This might be valid for the geometry of the upper part of the maar-diatreme volcano, especially for its crater, given that the number of individual eruptions can also heavily affect the final crater-diatreme morphology, and as many explosive events take place hence as large and old as your maar, the role of the substrate physical conditions will be reduced (e.g., [125]).…”

“…Recent analog experiments as well as field observations from classical diatremes cut into "soft substrate" showed that the diatreme wall can be steep for such maars that cut through soft substrate (e.g., [121][122][123][124][125]). This might be valid for the geometry of the upper part of the maar-diatreme volcano, especially for its crater, given that the number of individual eruptions can also heavily affect the final crater-diatreme morphology, and as many explosive events take place hence as large and old as your maar, the role of the substrate physical conditions will be reduced (e.g., [125]). In contrast, maars formed in hard-rock environment tend to be irregular, small in size and characterized by funnel-shaped and vertical (e.g., Joya Honda, Mexico [126], Nyos Maar, Cameroon [127]) to steeply dipping crater walls.…”