Description: Deception Island is the most active volcano in the South Shetland Islands with more than 20 explosive eruptions registered over the past centuries. The latest event (1970) was severely violent with a volcanic explosivity index (VEI) of 3. The column height reached 10 km, the estimated bulk eruptive volume was 〉 0.1 km3 and tephra fallout was reported as far as in King George Island (〉 150 km distance). In this work, we perform a compositional and textural analysis of the 1970 tephra layers found at Livingston Island’s glaciers. Results obtained are compared to the in situ pyroclastic deposits of the active vents during the eruption. The objective is to establish a correlation between the eruptive phases occurred during the 1970 event and the physicochemical features observed in the tephra deposits. This will be used the onset of future studies of tephra layers found in glaciers and marine/lacustrine sediment cores outside the island, improving our capacity to reconstruct the eruptive dynamics of past eruptions. This is fundamental to: (i) determine the size and explosiveness of past eruptions; (ii) assess the extent of their related hazards; (iii) complete the eruptive record; and (iv) consequently, perform accurate hazard assessments at the island. This work is part of the CSIC Interdisciplinary Thematic Platform (PTI) Polar zone Observatory (PTI-POLARCSIC) activities. This research was partially funded by the MINECO VOLCLIMA (CGL2015-72629-EXP) and HYDROCAL (PID2020-114876GB-I00) MCIN/AEI/10.13039/501100011033 research projects. Sampling was founded by CICYT (ANT91-1270, ANT93-0852 and ANT96-0734).

Description: Progressive hydrothermal alteration and mineral precipitation can modify the physical properties and mechanical behavior of the affected rocks, increasing the probabilities of phreatic or hydrothermal explosive eruptions. In this work we focus on the study of rock alteration and hydrothermal system of Deception Island, which is one of the most active volcanoes in Antarctica. A characterization of the pre-caldera and syn-caldera rock alterations has been done as a starting point for the understanding of the past and present hydrothermal system in the island. The alteration processes that have affected pre-caldera deposits are related to low temperature (〈200 oC) fluids, with pervasive palagonitisation and precipitation of smectite and zeolite. In some samples carbonate has also been detected. This alteration is consistent with rocks located at the first 500-600 meters depth of the pre-caldera shield volcano, in which the upper part of the sequence was affected by low-temperature acidic hydrothermal fluids that would have caused the dissolution of some phenocrysts and the consequent precipitation of magnesite. An extended palagonitisation characterize the syn-caldera deposits, but smectite and zeolite have also been identified. This is consistent with syn-depositional and meteoric alteration. Therefore, in the studied samples there is no evidence of persistent hydrothermal alteration that could be related to the current hydrothermal system. This work is part of the CSIC Interdisciplinary Thematic Platform (PTI) Polar zone Observatory (PTI-POLARCSIC) activities. This research was partially funded by the MINECO VOLCLIMA (CGL2015-72629-EXP) and HYDROCAL (PID2020-114876GB-I00) MCIN/AEI/10.13039/501100011033 research projects. This research is also supported by the PREDOCS-UB grant.