Ice-caves

Introduction

In volcanic environments, ice-caves and ice towers are the surface expressions of an established degassing area associated with fumarolic fields. In these contexts ice-caves are formed by warm gases and steam escaping from the lava flow surfaces which melt the bottom layer of overlying ice and snow leaving an underlying cavity which is accompanied by a typical chimney-like structure visible from the external ice-field.

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The known Antarctic volcanoes where ice caves have been observed are Mounts Erebus, Melbourne, Rittmann and Berlin (for the last, no exploration or studies are yet reported). While other ice caves have been observed in other volcanic regions, (the Cascade Volcanoes, USA, in Iceland, and in Kamchatka), nowhere else in the world hosts such a high concentration and diversity of such features, even if other ice-caves have been observed for example in the Cascade Volcanoes (Mt. Rainer).

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During the past two expeditions to Terranova Bay, mapping and gas and thermal monitoring conducted under the ICE-VOLC project have provided insights into the ice cave formation processes and the relationships between cave structures and magmatic processes. 

The ice caves on Mt. Melbourne and Rittmann studied in our project are created by the interaction of warm fumarolic gases and ice and snow layers, abundantly and permanently present near the thermal areas, where the maximum air temperature probably never rises above -10 °C.

Ice caves are formed by warm gases which melt the snow near the ground, often creating an intricate network of rooms and passages. Inside the ice caves there is a specific atmospheric circulation generated by a mixing of the warm fumarolic gases from the ground (mainly water and CO2) and the cold air coming from the outside. The main way of escape of the mixed gas circulating inside the cave is through the external chimney-like ice tower. Inside the cave, cold air arriving through small fissures or porosity of snow becomes warmer and enriched in volcanic gases rising up the slope of the volcano, and finally escapes from the ice tower chimneys.

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CO2 concentration inside a typical ice cave and air circulation/mixing.

The internal temperature tends to remain quite stable, however, this equilibrium is likely to be disturbed if the heat flux from the fumaroles within the cave changes as a result of changes to their source. Any variations in air circulation and gas composition within the cave are, therefore,  an indication of the possible onset of increased volcanic activity.. The specifically designed automatic geochemical monitoring station we propose to install within the cave will make the monitoring of any  such changes possible, enabling on the one hand a development in our understanding of  Melbourne volcanism while on the other an initial step towards an  early warning system for the nearby research bases.

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1. Ice-caves on Melbourne and Rittmann

Aurora ice-cave

MC3 ice-cave

MC8 – Hollow Ice Cave

2. Monitoring development and further studies

Melbourne volcano lies approximately 40 km north-northeast from MZS. Any potential unrest of this volcano may, therefore, significantly affect the base as well as the other two nearby scientific bases: Jon Bogo (Korea) and Gondwana (Germany), suggesting that a geochemical monitoring system is highly advisable. During the XXXIII expedition we deployed and tested an experimental geochemical automatic instrument coupled with a meteorological station, capable of monitoring the flux of heat, water and CO2 passing through the median portion of the Aurora cave. This represents a first step in establishing a permanent geochemical monitoring system. A future implementation of the above monitoring system will consist in the installation of a permanent station which will provide near real-time data able to recognize the evolution and changes in the state of the volcano, which can be highly useful for volcanic hazard mitigation.

A diagram of a possible monitoring system inside Aurora Ice Cave on Melbourne.

3. Photo gallery

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