Heat transfer and melting in subglacial basaltic volcanic eruptions: implications for volcanic deposit morphology and meltwater volumes

Abstract

Subglacial volcanic eruptions can generate large volumes of meltwater that is stored and transported beneath glaciers and released catastrophically in j6kulhlaups. At typical basaltic dyke propagation speeds, the high strain rate at a dyke tip causes ice to behave as a brittle solid; dykes can overshoot a rock-ice interface to intrude through 20-30% of the thickness of the overlying ice. The very large surface area of the dyke sides causes rapid melting of ice and subsequent collapse of the dyke to form a basal rubble pile. Magma can also be intruded at the substrate-ice interface as a sill, spreading sideways more efficiently than a subaerial flow, and also producing efficient and widespread heat transfer. Both intrusion mechanisms may lead to the early abundance of meltwater sometimes observed in Icelandic subglacial eruptions. If meltwater is retained above a sill, continuous melting of adjacent and overlying ice by hot convecting meltwater occurs. At typical sill pressures under more than 300 m ice thickness, magmatic CO2 gas bubbles form c. 25 vol% of the pressurized magma. If water drains and contact with the atmosphere is established, the pressure decreases dramatically unless the overlying ice subsides rapidly into the vacated space. If it does not, further CO2 exsolution plus the onset of H20 exsolution has the potential to cause explosive fragmentation, i.e. a fire-fountain that forms at the dyke-sill connection, enhancing melting and creating another candidate pulse of meltwater. The now effectively subaerial magma body becomes thicker, narrower, and flows faster so that marginal meltwater drainage channels become available. If the ice overburden thickness is much less than c. 300m the entire sill injection process may involve explosive magma fragmentation. Thus, there should be major differences between subglacial eruptions under local or alpine glaciers compared with those under continental-scale glaciers.

Transport and modification of glaciovolcanic glass from source to sink on Mars

“…1A,B) are found across a large variety of latitudes, ranging from volcanic fields near the poles to areas once covered by tropical mountain glaciers (Allen, 1979;Ghatan & Head, 2002;Head & Wilson, 2007;Hovius et al, 2008;Fagan et al, 2010;Martínez-Alonso et al, 2011;Scanlon et al 2014). Other common features include ridges known as tindars (Wilson & Head, 2002;Chapman et al, 2003;Komatsu et al, 2004;Zealey, 2009;Pedersen et al, 2010), which dominate in the neovolcanic zones of Iceland (Jakobsson & Gudmundsson, 2008). With the exception of the subaerial lavas, both tuyas and tindars contain comparable facies (Fig.…”

Shape, rheology and emplacement times of small martian shield volcanoes

“…It is thus not possible to conclude with confidence about the evolution of effusion rate with time. Furthermore, it is of note that effusion rates and viscosities should be related, following the expression of Wilson and Head (2002):…”

Volcano-Ice Interaction as a Microbial Habitat on Earth and Mars

“…particularly through the generation of hydrothermal systems (Chapman et al, 60 2000;Head & Wilson 2002; Schulze-Makuch et al, 2007). It has previously been 61…”

“…Differences in localized 55 lithospheric heat flow and crustal thermal properties are likely to result in spatial 56 variation in the cryosphere thickness (Clifford 2010). This cryosphere, coupled 57 with volcanic activity, has the potential to produce several kinds of environments 58 for life on Mars with a wide range of thermal and chemical conditions, 59particularly through the generation of hydrothermal systems (Chapman et al, 60 2000;Head & Wilson 2002; Schulze-Makuch et al, 2007). It has previously been 61…”

“…124 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 and widely distributed source of ice (Clifford et al, 2010). Therefore, it is highly 136 probable that these major processes have interacted in the past (Chapman et al, 137 2000;Head & Wilson 2002) and may even continue to do so today deep within 138 the subsurface (Schulze-Makuch et al, 2007). As a result, volcano -ice 139 interaction may represent an environment that has persisted over a significant part 140 of martian history.…”