Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 Introduction: volcano-ice interaction on Earth and Mars JOHN L. SMELLIE j & MARY G. CHAPMAN 2 1 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB30ET, UK (e-mail. JLSM@ bas.ac, uk) 2 US Geological Survey, 2255 N. Gemini Drive, Flagstaff, Arizona 86001, USA (e-mail: mchapman@ usgs.gov) The theme of this volume was conceived dur- martian examples? There is no simple answer ing discussions between the editors and many to that question, but the papers in this volume colleagues, particularly Ian Skilling, Magnus are an important step forward. The purpose Gudmundsson, Virginia Gulick and Sveinn of the volume is to provide a snapshot of cur- Jacobsson, in response to a burgeoning growth rent research in volcano-ice interactions. Until of interest in volcano-ice systems by geologists we understand the similarities and differences working on terrestrial and putative martian between processes that occur on Earth and examples. Both communities of geologists have Mars, it is unwise to transfer blindly Earth- been travelling essentially parallel paths in pur- based knowledge to interpreting remote martian suit of their science, but using very different tools: systems. principally remote sensing (satellite data) for Mars; mainly outcrop geology for Earth studies. At present, there are no publications that span the Eruptive, hydrological and glacial divide that artificially exists between the terres- dynamics, and tephra chronology of trial and martian investigations, and, thus, the subglacial eruptions concept for this volume was borne. Isolated papers have addressed volcano-ice topics but The first two contributions are complementary this is the first attempt to assemble a thematic theoretical syntheses of magma-ice interactions group of contributions addressing the diverse on Earth and Mars. For Earth, Wilson & Head range of interactions known or thought to occur show how, at the very high strain rates antici- on both planets. pated, an advancing dyke tip will propagate at The broad focus of this volume is the interac- least 20-30% into the thickness of an overlying tion between magmas and cryospheres, whether ice sheet before collapsing to form a basal rubble. on Earth or Mars. On Earth, snow and ice are Other intrusions will spread sideways to form a found in extensive polar ice caps and on the sill at the ice-substrate interface. Their analysis summits of mountains even down to tropical also suggests that the course of an eruption is latitudes, and ice sheets were much more wide- determined by the fate of any meltwater formed. spread in the geological past. The exploration of If it drains, explosive fragmentation may be Mars, by satellite and instrumental lander, has triggered leading to further enhanced ice melting. also revealed abundant examples of water and These results have important implications for ice: in polar ice caps today and formerly else- subglacial lava effusion and flow morphology, where on the surface, in the crust and in the and some sills may be intruded largely as megaregolith, and the planet may even have hyaloclastite breccias. Head & Wilson review sustained frozen oceans early in its history. Very the distribution of water and ice on Mars. They different eruptive environments are implied, how- show how the wide range of eruption styles ever, with Mars experiencing about a quarter of differs from those on earth because of modula- Earth's gravity and a much thinner atmosphere. tion by the martian environment. A major These are physical properties that significantly difference is the presence on Mars of a several affect the basic principles of magma ascent and km-thick global permafrost layer in the upper eruption, leading to large differences in eruptive crust. In particular, generation of mega-lahars styles on both planets. The question arises: to may be a unique martian eruptive phenomenon. what extent do terrestrial volcano-ice interac- Latitudinal variations in the availability of cryo- tions provide a plausible analogue for putative spheric water with time may also have caused From: SMELLIE, J. L. & CHAPMAN, M. G. (eds) 2002. Volcano-Ice Interaction on Earth and Mars. Geological Society, London, Special Publications, 202, 1-4. 0305-8719/02/$15.00 © The Geological Society of London 2002. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 2 J.L. SMELLIE & M. G. CHAPMAN evolutionary changes in volcanic morphology sive ice cap, and the volcano probably grew and eruption styles, which can be used as clues to mainly during periods of deglaciation. By con- ancient palaeolatitudes. There are few well- trast, from studies by Edwards & Russell, Kelman, observed and documented subglacial eruptions Russell & Hiekson and Tnffen, MeGarvie, Gil- on Earth, that of Gjfilp (Iceland) in 1996 being bert & Pinkerton, it is now apparent that the best example. However, Smellie describes an subglacial eruptions of more evolved magmas earlier eruption of an Antarctic volcano, in 1969, show significant differences in volcano construc- which crossed a thin ice cap on Deception Island tion compared with those at basaltic centres. and was also well documented. Unusually, the Centres in British Columbia (Hoodoo Moun- eruption was associated with widespread supra- tain: phonolites-trachytes; Garibaldi Volcanic glacial sheet flooding as meltwater overflowed Belt: andesites-dacites), and in Iceland (Rau6u- from ice fissures and chimneys above the erupt- fossafj611: rhyolites) are lava flow-dominated. ing vents. He invokes gas-driven melting of Early-formed clastic products are not well an essentially 'dry' cavity roof to explain the known but, exceptionally, vigorous phreatomag- enigmatic speed with which subglacial eruptions matic explosions were a feature of the Rau6u- of relatively fluid magma can melt through fossafj611 edifice and built a pile of unbedded ash substantial thicknesses of overlying glacier ice. up to 300m thick. Later phases in all these Larsen completes the section with a statistical volcanoes involved compound lava flows em- summary of 11 centuries of eruptions from Ice- placed within essentially dry ice cauldrons. Flow landic volcanoes. She shows that a minimum of and edifice shapes were strongly influenced by 60% were from partly ice-covered and ice- ponding against surrounding thick masses of ice. capped volcanic systems. It is postulated that the differences between subglacial rhyolitic and basaltic eruptions are principally caused by contrasting hydrological patterns. Subglacially erupted lithofacies at two Reconstruction of sub-ice volcanoes and ice stratovolcanoes in Marie Byrd Land (Antarctica) sheet thicknesses from geomorphological and are interpreted by Wileh & Melntosh and provide lithofacies analysis and volatile compositions evidence for the existence of a widespread mid- Miocene ice sheet, and Miocene-Pleistocene ice- In this section, Skilling reviews and describes the level changes in West Antarctica. Together with lithofacies, depositional processes and architec- extensive 4°Ar/39Ar dating, the sequences pro- ture of basaltic lava-fed deltas. It is the most vide a uniquely detailed proxy record and chro- comprehensive published account of the con- nological framework for the glacial history of struction of these morphologically distinctive and the region. They urge caution in interpreting common subglacial volcanic features. Despite former ice levels from volcanic sequences unless superficial similarities with alluvial deltas, there features such as coastal proximity and local are important contrasts, particularly the absence palaeotopography are also taken into account, of any effluent force and presence of hot clasts and they speculate about a link between incep- in the volcanic systems. LeMasurier describes tion of a dynamic West Antarctic Ice Sheet and basaltic and trachytic lava-fed deltas in Marie increased volcanism in Marie Byrd Land. In a Byrd Land (Antarctica) and focuses particularly unique study in this volume, Dixon, Filiberto, on documenting superbly exposed post-deposi- Moore & Hiekson measured dissolved volatile tional structures. He also highlights an anom- concentrations (H20, CO2, S and C1) in tholeiitic alous apparently province-wide lack of pillow and alkali basaltic glasses from Tanzilla Moun- lava cores in Marie Byrd Land subglacial volca- tain, a subglacial volcano from British Colum- noes, and suggests that the presence of abundant bia. The edifice was erupted entirely subglacially microlites in the erupted lavas might have altered and the vapour saturation pressures suggest for- the magma rheology and inhibited pillow forma- mer ice thicknesses within the range 300-900 m tion. Loughlin describes the very wide range consistent with eruption during the waning of lithofacies involved in the construction of a phases of the coeval Fraser glaciation. single, large, long-lived alkali basalt stratovol- cano (Eyjafjallaj6kull, Iceland). The volcano is dominated by subaqueous lithofacies emplaced under relatively thin ice (< 150 m), in associations Remote sensing of terrestrial and martian bounded by glacial unconformities representing subglacial features significant time gaps formed during glacial advances. Most deposits were formed beneath Data from instruments on the currently orbiting valley-confined glaciers, others beneath an exten- Mars Global Surveyor spacecraft indicate the Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021