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Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica. In the 1988–1989 austral summer, after the most recent eruptive process on the island (1967–1970), monitoring of volcanic activity through geophysical and geodetic techniques was resumed by Spanish and Argentinean scientists. In order to monitor the island's tectonic and volcanic behavior, a geodetic network was deployed. Currently, this network consists of 15 geodetic benchmarks located around Port Foster, Deception's inner bay open to the sea. Two additional geodetic benchmarks were installed outside Deception Island to be used as reference benchmarks for the differential positioning strategy. Since 1991–1992, geodetic ground-displacement velocities between the successive austral summer Antarctic campaigns have been computed and analyzed. The overall geodynamic behavior of Deception Island within the South Shetland Islands, Antarctic Peninsula and Bransfield Basin regional environment has been analyzed from geodetic ground-displacements. Results obtained demonstrate that Deception and Livingston island have a similar behavior derived from the Bransfield Basin extension and the Phoenix micro-plate subsidence processes. However, Deception Island is also highly influenced by its volcanic activity. Deception Island's volcanic behavior between 1991 and 2018 is shown by the velocity field, strain tensors and pressure source evolution obtained from the ground-displacements at the geodetic benchmarks. During this time period, it is possible to identify different inflation and deflation phases separated by transitional (or mixed) stages of extension without uplift and compression without subsidence. The most representative inflation and deflation periods were analyzed in detail, to show how they correlate with high and low seismic activity, respectively. The transitional or mixed stages, seem to be the precursors of the next inflation or deflation phase being the Bransfield basin rifting and NW-SE extension the potential related process. Finally, we have analyzed the processes that occurred prior to the volcanic unrests of 1999–2000 and 2012–2013. In both cases, an increase in detected seismic activity and/or soil and seawater temperature was observed and a mixed phase of extension without uplift seems to be precursory to the volcanic unrest. The correlation between the inflation processes, identified by ground-displacement of the network geodetic benchmarks, the increase in seismicity and the increment of soil and seawater temperature makes these transitional mixed phases potential precursors of Deception Island's volcanic unrest periods. © 2019 Elsevier B.V.

After the 2004 unrest on Tenerife (Canary Islands), the Global Navigation Satellite System (GNSS) network called TEGETEIDE was designed and deployed with seven survey mode stations to contribute to a volcanic alert system. Starting in 2008, public access data from continuous GNSS stations, managed by public institutions, were included in this network allowing measurement of ground displacement at 14 locations in Tenerife. Data acquired from 2005 to 2015 was analysed to assess ground deformation in Tenerife following the 2004 volcanic unrest. The overall ground deformation depicted compression in the central Las Cañadas Caldera possibly caused by gravitational subsidence of the high central volcanic cone. This sinking is generalised around the whole island but is less in the northeast (Anaga Massif) where we found an extension rate close to 200 strain/y that could be related to a secondary submarine fault accommodating rifting to the northeast and isolating the behaviour of this massif. At the south volcanic field (south rift), another localized area with an extensional deformation was detected, possibly resulting from the subsurface fluid migration or mass addition that caused the 2004 volcanic unrest because is located following the seismic swarm alignment along Icod Valley towards Roque del Conde massif that persists since that event. We also detected residual plate velocity indicating movement of Tenerife towards Gran Canaria that should be studied in the context of the entire Canary Islands archipelago., This research has been partially funded by the projects TEGETEIDE (CGL2004-21643E), METOTEIDE (CGL2005-25066E), VOLRESTE (CGL2009-MEC) and PEVERTE (CGL2011-28682-C02-01) as well as the 200430E438 CSIC project.

Increased thermal activity was detected to coincide with the onset of volcano inflation in the seawater-filled caldera at Deception Island. This thermal activity was manifested in pulses of high water temperature that coincided with ocean tide cycles. The seawater temperature anomalies were detected by a thermometric sensor attached to the tide gauge (bottom pressure sensor). This was installed where the seawater circulation and the locations of known thermal anomalies, fumaroles and thermal springs, together favor the detection of water warmed within the caldera. Detection of the increased thermal activity was also possible because sea ice, which covers the entire caldera during the austral winter months, insulates the water and thus reduces temperature exchange between seawater and atmosphere. In these conditions, the water temperature data has been shown to provide significant information about Deception volcano activity. The detected seawater temperature increase, also observed in soil temperature readings, suggests rapid and near-simultaneous increase in geothermal activity with onset of caldera inflation and an increased number of seismic events observed in the following austral summer.

The South Shetland Islands archipelago is dynamically complex due to its tectonic surroundings. Most islands are part of a formerly active volcanic arc, although Deception, Penguin and Bridgeman Islands, as well as several submarine volcanoes, are characterized by active back-arc volcanism. Geodetic benchmarks were deployed and the movement of the lithosphere to which they were fixed measured to provide geodynamic insight for the South Shetland Islands, Bransfield Basin and Antarctic Peninsula area based on surface deformation. These benchmarks' data add spatial and temporal coverage to previous results. The results reveal two different geodynamic patterns, each confined to a distinct part of the South Shetland Islands archipelago. The inferred absolute horizontal velocity vectors for the benchmarks in the northeastern part of the archipelago are consistent with the opening of the Bransfield Basin, while benchmark vectors in the southwestern part of the archipelago are similar to those of the benchmarks on the Antarctic Peninsula. In between, Snow, Deception and Livingston Islands represent a transition zone. In this area, the horizontal velocity vectors relative to the Antarctic plate shift northeastwards from N to NW. Furthermore, the South Shetland Islands benchmarks, except for that at Gibbs (Elephant) Islands, indicate subsidence, which might be a consequence of the slab roll-back at the South Shetland Trench. In contrast, the uplift revealed by the Antarctic Peninsula benchmarks suggests glacial isostatic adjustment after the Larson B ice-shelf breakup., This geodetic research has been carried out with the support of the Spanish Ministry of Education and Science as part of the National Antarctic Program. The following research projects contributed directly to this work: “Recognition and fast evaluation of volcanic activity on Deception Island (GEODESY) (ANT1999-1430-E/HESP)”; “Geodetic Studies on Deception Island: deformation models, geoid determination and Scientific Information System (REN2000-0551-C03-01/ANT)”; “Acquisition of scientific software for GPS data processing (REN2000-2690-E)”; “Geodetic Control of the volcanic activity of Deception Island (CGL2004-21547-E/ANT)”; “Update of the Spanish Cartography for Deception Island (CGL2004-20408-E/ANT)”; “Volcano-tectonic activity on Deception Island: geodetic, geophysical investigations and Remote Sensing on Deception Island and its surroundings (CGLl2005-07589-c03-01/ANT)”; and “Geodetic and Geothermal Researches, Time Serial Analysis and Volcanic Innovation in Antarctica (South Shetland Islands and Antarctic Peninsula (GEOTINANT) (CTM2009-07251/ANT))”.