REEVALUATING CRYOLAVA FLOW EMPLACEMENT: FEASIBILITY OF TUBES

Lava tubes are a phenomenon familiar in terrestrial volcanology where channelized lava flows cool, creating a roof which insulates the interior allowing for transport over much longer distances. The processes that control lava tube formation are dominated by fluid dynamic evolution, heat transport, and thermomechanical erosion of the substrate. These processes exist on icy bodies in the outer solar system in different temperature and compositional regimes.

Cryolava tubes have been mentioned in some studies as a morphology or emplacement mechanism. While mentioned casually in the literature, no studies have directly investigated whether cryolava tubes are feasible and what form they would take. We modified existing lava tube models for the temperature and compositional regimes of icy bodies, to assess whether tube formation is likely, and to interpret their efficiency as an emplacement mechanism.

Eruption into the low-pressure environments of many icy bodies causes rapid boiling and crystallization which increases viscosity several orders of magnitude (e.g. for water, 1.5 mPas to 15 Pas). At such low viscosity, cryolava flows will be dominantly turbulent even to large crystal fractions. This suggests the evolution is more like slushie formation than a freezing river, and crust formation is not as simple as an ever-thickening ice layer. High volume, effusive (flood?) eruptions would be required to overcome the rapid solidification in the cold, low-pressure environment.

Once formed, cryolava tubes are less likely to be preserved than their terrestrial silicate counterparts. Water ice is much more ductile than silicate glass or rock, with much shorter relaxation times, suggesting only geologically recent tubes would be observed. Cryolava tubes, once drained, may allow cave-like networks to form on icy worlds. If exposed at the surface, these caves could provide passage into the subsurface of the cryosphere making them high priority astrobiological and habitability targets.