Heat source or heat sink: What dominates behavior of non-explosive magma-water interaction?

Abstract

[1] Much of the volcanism on Earth takes place in subaqueous settings where magma has direct contact with a water reservoir of restricted or quasi unrestricted volume. In order to assess the intensity and timescale of non-explosive interaction of magmatic melts and water, experiments representing these settings were performed. Natural volcanic samples were remelted and poured as a continuous jet into a water-filled calorimeter where the melt interacts with its coolant. The rapid cooling results in granulation, i.e. brittle failure of the material. Granulation needs energy, which is taken from the thermal input of the hot melt. Energy used in granulation was found to require 5%-20% of the melt's initial heat content. This energy loss fraction is insensitive to variations in coolant-and melt temperatures but instead depends on the melt's thermomechanical properties. However analysis of the experimentally produced granulate indicates a strong correlation between the initial coolant temperature -i.e. the heat sink-and the grain-size distribution, but also shows variations due to material properties. The maximum of the grain-size distribution was determined to change from a diameter of 1 mm up to 4 mm due to coolant temperature increase. Properties of the heat source (melt ) dominate the efficiency of the process, whereas both heat sink and source characteristics determine the products.

External surface water influence on explosive eruption dynamics, with implications for stratospheric sulfur delivery and volcano-climate feedback

“…The mixing of water, steam, pyroclasts, and lithic debris in the vent region in explosive hydrovolcanic eruptions is complex and may involve effects of shocks, supersonic flow, film boiling, and multiple fragmentation mechanisms (Wohletz et al, 2013;Houghton and Carey, 2015;van Otterloo et al, 2015) that introduce inherently time-dependent and three-dimensional mechanisms for entrainment and mechanical stirring that are not captured in a one-dimensional steady-state integral model. However, following extensive studies of entrainment and mixing into turbulent plumes (Morton et al, 1956;Linden, 1979;Turner, 1986), a recent complementary analysis of water entrainment into supersonic, submerged gas jets (Zhang et al, 2020) and studies of the bulk energetics of interactions between hot pyroclasts and water (Dufek et al, 2007;Mastin, 2007a;Schmid et al, 2010;Sonder et al, 2011;Dürig et al, 2012;Woodcock et al, 2012) we can parameterize these processes to explore effects on total budgets for mass, energy, and buoyancy. Following Morton et al (1956); Kaminski et al (2005); Carazzo et al (2008); Zhang et al (2020), we will relate the radial entrainment speed of water or atmosphere to the local rise speed of a jet and prescribe resulting velocity, pressure and temperature fields.…”

“…Wohletz, 1983;Büttner et al, 2002Büttner et al, , 2006Mastin, 2007a;Woodcock et al, 2012;Patel et al, 2013;Liu et al, 2015;van Otterloo et al, 2015;Fitch and Fagents, 2020;Dürig et al, 2020b;Moitra et al, 2020). However, with a specified magmatic heat flow at the vent, considerations of the surface energy consumed to generate fine ash fragments (Sonder et al, 2011), guided by published experiments along with observational constraints on the hydromagmatic evolution of particle sizes (Costa et al, 2016), provide a way forward that is appropriate for a 1D integral model. Figure 3 highlights the salient features of the fragmentation model, using the example of a single simulation with q c = 1.03 × 10 8 kg/s and Z e = 120 m. Sonder et al (2011) performed lab experiments submerging molten basalt into a fresh water tank to constrain the partitioning of thermal energy lost from the melt between that which is transferred from melt to heat external water and that which is consumed irreversibly through fracturing of the melt to generate new surface area and fine ash.…”

“…Since we assume that the energy consumption during quench fragmentation results from the generation of new surface area (Sonder et al, 2011;Dürig et al, 2012;Fitch and Fagents, 2020), we calculate the specific surface area at each particle bin size assuming spherical particle geometry,…”

Meter-Scale Experiments on Magma-Water Interaction

“…The reason for different fragmentation mechanisms in these considerations may be related to the different applied melt-water interaction scenarios: The main application scenario for reactor safety considers a melt jet falling into and interacting with a relatively large pool of water (Dinh et al, 1999;Manickam et al, 2016), which is different from the entrapment of water domains by a melt. In the case of silicate melts, however, the jet-falling configuration only rarely leads to explosive interaction, but to lower energy thermal granulation and the production of glassy rinds (Mastin, 2007;Schmid et al, 2010;Sonder et al, 2011). An example of a rare explosive event when melt enters a large water body is the widely reported small-scale explosive incident at the ocean entry of Kilauea's recent lava flow (fissure #8) activity, where a tourist boat was hit by an ejected lava bomb.…”

Meter‐Scale Experiments on Magma‐Water Interaction

“…The reason for different fragmentation mechanisms in these considerations may be related to the different applied melt‐water interaction scenarios: The main application scenario for reactor safety considers a melt jet falling into and interacting with a relatively large pool of water (Dinh et al, ; Manickam et al, ), which is different from the entrapment of water domains by a melt. In the case of silicate melts, however, the jet‐falling configuration only rarely leads to explosive interaction, but to lower energy thermal granulation and the production of glassy rinds (Mastin, ; Schmid et al, ; Sonder et al, ). An example of a rare explosive event when melt enters a large water body is the widely reported small‐scale explosive incident at the ocean entry of Kilauea's recent lava flow (fissure #8) activity, where a tourist boat was hit by an ejected lava bomb.…”