Cryomagma ascent on Europa

Abstract

Europa's surface exhibits morphological features which, associated with a low crater density, might be interpreted to have formed as a result of recent cryovolcanic activity. In particular, the morphology of smooth deposits covering parts of the surface, and their relationship to the surrounding terrains, suggest that they result from liquid extrusions. Furthermore, recent literature suggests that the emplacement of liquid-related features, such as double ridges, lenticulae and chaos could result from the presence of liquid reservoirs beneath the surface. We model the ascent of liquid water through a fracture or a pipe-like conduit from a subsurface reservoir to Europa's surface and calculate the eruption time-scale and the total volume extruded during the eruption, as a function of the reservoir volume and depth. We also estimate the freezing time of a subsurface reservoir necessary to trigger an eruption. Our model is derived for pure liquid water and for a briny mixture outlined by Kargel (1991): 81 wt% H 2 O + 16 wt% MgSO 4 + 3 wt% Na 2 SO 4 . Considering compositional data for salt impurities for Europa, we discuss the effect of MgSO 4 and Na 2 SO 4 on the cryomagma freezing time-scale and ascent. For plausible reservoir volumes and depths in the range of 10 6 m 3 ≤ V ≤ 10 10 m 3 and 1 km ≤ H ≤ 10 km respectively, the total extruded cryolava volume ranges from 10 3 m 3 to 10 8 m 3 and the duration of the eruptions varies from few minutes to few tens of hours. The freezing time-scale of the cryomagma reservoirs varies with cryomagma composition and the temperature gradient in the ice shell: from a few days to a thousand years for pure water cryomagma, and from a few months to a 10 4 years for briny cryomagma.

Tidally Heated Convection and the Occurrence of Melting in Icy Satellites: Application to Europa

“…The fate of these putative melt pockets is, however, difficult to determine. For such shallow depths, it is possible that part of the melt reaches the surface (Lesage et al, 2020;Mitri et al, 2008;Showman & Han, 2004), while most of the melt probably sinks to the subsurface ocean via percolation through the solid ice matrix (Kalousová et al, 2014(Kalousová et al, , 2016. The occurrence of these melt pockets may therefore favor material exchange between the subsurface ocean, the ice layer, and potentially the surface.…”

“…Several mechanisms have been proposed to overcome this difficulty. For instance, the transport of melt to the surface may be triggered by fractional crystallization (Mitri et al, ) or pressurization (Lesage et al, ; Showman & Han, ). Importantly, and regardless of the mechanism considered, the presence of liquid reservoirs close to the surface is required.…”

Brine Migration and Impact‐Induced Cryovolcanism on Europa

“…(1) The dominant salt is either NaCl or MgSO 4 , which represent the likely end-members of ocean-derived impurities within Europa's ice shell based on spectroscopic observations (Brown & Hand, 2013;Fischer et al, 2015;Hand & Carlson, 2015;McCord et al, 1999McCord et al, , 2001Trumbo et al, 2019). (2) Only 1% of the volume of the final melt pocket erupted onto the surface as suggested by numerical models (Lesage et al, 2020), and the depression measurable by the DTM has the same volume. (3) The complete slush reservoir within the crater has been reprocessed by melt pocket migration.…”

The Salty Secrets of Icy Ocean Worlds

“…It should be noted that the authors acknowledge the limitations of their work in this example, as they neglect the formation of eutectic hydrate phases. Another effect not taken into account, especially important in the case of shallow liquid pockets, is the volume variations during freezing that can build up pressure in closed liquid pockets within the ice shell, enough to possibly trigger extrusion of cryo‐magmas (Lesage et al., 2020).…”