THIS POST IS A CRITICAL REVIEW OF A JUNE 2019 EL PAIS ARTICLE IN CHILE ON ANTARCTICA DESCRIBED AS THE HEART OF GLOBAL WARMING: LINK TO SOURCE: https://english.elpais.com/elpais/2019/04/26/inenglish/1556263201_477143.html

PART-1: WHAT THE SOURCE ARTICLE SAYS

Scientists come here to Antarctica to wrestle with the complexities of the impact of climate change on Earth. If the whole of Antarctica were to melt, the sea level would rise by 60 meters, enough to submerge all of Europe. This is not likely to happen but less dramatic developments are already in progress. Glacial retreat is affecting the marine ecosystems.

Antarctica regulates natural processes on a global scale. It is the beating heart of the planet, and every year its surface changes across 14 million square kilometers due to ice fluctuation. Antarctica is connected to almost all the seas on the planet. It influences the agricultural cycle in China, the monsoon flooding in Vietnam, the prevailing pattern of water flows in Australia, and also extreme weather events in South America.

Antarctica is divided into three main areas. These are East Antarctica, West Antarctica, and the Antarctic Peninsula. The Antarctic Peninsula is where that the average temperature has risen most dramatically and where most of the ice is being lost. This ice loss here has tripled in the last 30 years. Global warming is most obvious here in the Antarctic Peninsula where glaciers are melting much faster and the water salinity is changing. Wherever there is a lot of glacial melt the salinity decreases and puts native water creatures at risk. This assault on nature is a creation of global warming.

Chinstrap penguins are found in the Deception Island Collapse Caldera located in the Shetland Islands where the Spanish research bases are located. There, the number of Chinstrap penguins have dropped by 41% over the study period. This is because Chinstrap penguins feed on krill and the krill population there has dropped by 80% because of falling salinity caused by melting ice which in turn is caused by global warming. The Gentoo penguin also feed on krill and squid and other fish but these guys are growing in numbers and expanding their territory. These are the dynamics of ecosystems in the process of change.

Carjaval is the Chilean base in Antarctica. Despite its remoteness, climate change has reached here with tragic consequences. For example, one of the scientists fell down a crack in the ice. The crack was created by global warming ice melt. Global warming is increasing the size of the cracks in the Fuchs glacier that are not visible from the surface.

The future of Antarctica beyond 2048 as shaped by climate change is difficult to predict. Our grandchildren may see Antarctica as it is today but not our great-grandchildren because the longer the time span of our predictions, the less we know, and the less we know the the more catastrophic our predictions get.

TOURISM: Although there are many research stations here (see footnote below), more than 90% of the people who come herfe are tourists. About 50,000 tourists a year visit Antarctica. Some come on small cruise ships and others fly from Chile or Argentina. They spend the day on a rubber dinghy doing a tour of the South Shetland Islands that act as the gateway to the continent. A significant tourist destination is the Deception Island Collapse Caldera shown below. A collapse caldera forms when an extremely powerful volcanic eruption blows the top of the volcano out and leaves a bowl-like lake filled with hot springs water kept warm by geothermal heat from below. This water used to be ice.

CLIMATE CHANGE

Predicting the impact of climate change in Antarctica is devilishly difficult. The climate simulation models that predict the response to climate change and which are crucial to our understanding of the effects of global warming fail spectacularly on this continent. But there are signs that the Antarctic is already affected by climate change, though the evidence is rather more subtle than in other regions.

The Antarctic peninsula has the distinction of being one of the places where the temperatures have risen the most since the 1950s: around 2.5º, three times more than on the planet overall. For the first 15 years of this century, temperatures dropped due to local wind patterns but have risen again in the last few years. “There is no simple message in the Antarctic the way there is in the Arctic, where the effects of global warming are much clearer; the changes here are more subtle.

The advance or retreat of the glaciers on a global level is found in satellite data. The problem here is that the margin of error is around 15 cm which is more or less the same as what certain areas can lose or gain, and that makes it very hard to establish what is happening. Since the start of this century Antarctica is said to have lost around 220 gigatons of ice every year. The effect of this melted ice is a rise in the global sea level of 0.6 millimeters a year.

Earth’s non-polar glaciers lose around 335 gigatons a year, triggering a global sea level rise of 0.9 mm/year. The Arctic and high mountain glaciers are more susceptible to climate change as they do experience temperatures above freezing but this is not the case in Antarctica where the temperature range is -60C to -10C.

The loss of ice in the Antarctic takes place mainly on the peninsula and in the west of the continent where enormous glaciers stretch from the land into the sea in vast barriers. These glaciers present the highest risk for the future as masses of warm water have been seeping for some years now below the ice and melting them from underneath. The Pine Island glacier has retreated 12 or more kilometers since records began and rate of retreat is accelerating.

The picture gets increasingly complicated in the east, where the glaciers on the mountains are far more stable. “For decades, an increase in ice was recorded but in the last few years, the first signs have emerged of some of the glaciers here are thinning down.

It difficult to establish whether the ice melt in the Antarctic is due to human activity and the effects of emissions, or whether it is part of a natural cycle. The terrestrial ecosystem is complex and interconnected. For processes on this scale, you can’t discount natural causes which in certain specific glaciers or certain developments could be the predominant factor. At the same time, human interference in natural cycles over the course of last century is generally undeniable. {confirmation bias: “and therefore it has to be there somewhere and if we look hard enough we will find it”}

Whatever the cause of the observed ice melt in Antarctica, there is no sign of the ice melt stopping. It is very likely that the glaciers on the Antarctic peninsula and the west of the continent will continue to lose mass and there is also some concern that the glaciers in the east will also lose ice. By the end of this century average temperatures could have risen by between 2º C and 4º C. which means that it will still be below freezing. Therefore the complete collapse of Antarctic’s ice with a seal level rise of 60 meters is not possible by way of global warming. Yet, scientists still worry that IF liquid water forms underneath the ice some kind of feedback melting process could still be the sea level rise catastrophe that we are worried about.

FOOTNOTE: A list of Antarctica research stations provided by worldatlas.com : There are two types of stations – permanent and seasonal. Permanent stations are are maintained by Argentina, Australia, New Zealand, Belgium, Chile, Brazil, France, Germany, and Italy, the UK, the USA, Russia, India, South Africa, and China. Some of these countries have multiple stations. This is the new cool thing for emerging nations to do so this list is likely to be incomplete and will change in the coming years. It’s a prestige thing. Places like Dubai and Iran are waiting in the wings.

Argentina has a total of six active research stations operating all the year round. Some of its permanent research stations include Esperanza base in the Hope Bay, Marambio base, Orcadas, and Belgrano II. These four stations are in the south of 60 degrees of the Antarctic.

Australia also has its Mawson research station located south of Antarctica. It lies in the Holme Bay. It is Australia’s oldest Antarctic station base for research programs such as cosmic rays detectors, aeronomy, and meteorological and geomagnetic studies. The station houses around 20 personnel during winter, and as many as 60 personnel during summer, and is the only station that uses wind generators for 70% of its electrical power needs.

Belgium is known for the Prince Elizabeth Antarctica research station. It is built and operated by the International Polar Foundation and combines eco-friendly material, efficient energy use, and a modern waste management system. The station is run entirely on the wind and solar energy and mainly focuses on the investigations and research on ice related projects.

Brazil has its Comandante Ferraz Antarctica Station located in the Admiralty Bay. The station is primarily used to study programs related to climate change such as ozone depletion, global warming, greenhouse effects, and ocean’s rising levels. In 2012, a fire burnt down around 70% of the station, killing two soldiers in the process.

CRITICAL COMMENTARY

In a related post LINK: https://tambonthongchai.com/2019/06/27/antarctica/ we describe significant geological features in West Antarctica (that includes the Antarctic Peninsula and the Shetland Islands) in terms of the West Antarctic Rift System (WARS) and the Marie Byrd Mantle Plume. These geological features are associated with volcanic activity and significant geothermal heat, enough to explain ice melt events there.

At the same time we find in yet another related post LINK: https://tambonthongchai.com/2020/10/27/globalwarming-1979-2020/ that {The oddities of the Polar Regions are that the North Polar region is warming the fastest with a mean annual full span warming rate of all calendar months of 0.0250C/year while the South Polar Region is warming the slowest with a negative warming so that it is actually cooling at an rate of 0.009C/year. The corresponding rates for Global warming are: Global land and ocean = 0.0138C/year, Global land only is higher at 0.0187C/year, and Global ocean only correspondingly lower at 0.0199C/year. Of the other three regions, the Northern Extent is warming the fastest at a rate of 0.0183C per year with the Tropics at 0.0132/year and the Southern Extent warming at the lower rate of 0.01C per year}.

These data taken together do not support the climate science research agenda in Antarctica in which climate science appears determined to find a causal connection between anthropogenic global warming (AGW) and ice melt in Antarctica.

The research questions and the research methodology used contain the confirmation bias that observed ice melt in Antarctica and its sea level rise implication are caused by AGW such that the causation of these horrific events can be traced to the combustion of fossil fuels implying that therefore they can and must be attenuated by taking climate action in the form of reducing fossil fuel emissions. The issue of confirmation bias in climate change research is explored in a related post; LINK: https://tambonthongchai.com/2018/08/03/confirmationbias/

Yet another issue in this attribution is that it involves episodic and geographically isolated ice melt events. The time and geography constraints imply that they can only be understood as INTERNAL CLIMATE VARIABILITY (ICV) and that therefore they cannot be related to AGW. The internal variability issue is described in a related post: LINK: https://tambonthongchai.com/2020/07/16/the-internal-variability-issue/

Geothermal heat generation in West Antarctica from the geological features described in the related post are presented in the relevant bibliography below. Good evidence is found in this literature of significant geothermal heat flux in the region that provide a better explanation of ice melt events there than AGW.

WE CONCLUDE FROM THIS ANALYSIS THAT ICE MELT EVENTS IN ANTARCTIA ARE EPISOIDIC AND LOCALIZED TO KNOWN GEOLOGICALLY ACTIVE REGIONS AND THAT THEREFORE EPISODIC AND LOCALIZED GEOTHEMAL ACTIVITY PROVIDES A BETTER EXPLANATION FOR THESE EVENTS THAN AGW CLIMATE CHANGE. THE EXTREME EFFORT FOUND IN CLIMATE SCIENCE TO RELATE ANTARCTIC ICE MELT EVENTS AND THEIR SEA LEVEL RISE IMPLICATIONS TO HUMAN CAUSE BY WAY OF AGW CLIMATE CHANGE IS THEREFORE BEST UNDERSTOOD AS A FORM OF CONFIRMATION BIAS DRIVEN BY ADVOCACY. THE CHILEAN VERSION PRESENTD ABOVE IS A PARTICULARY MILD FORM OF THIS PRACTICE AS THEY APPEAR TO ADMIT TO THE DIFFICULTIES OF THAT ATTRIBUTION DESCRIBED IN OUR ANALYSIS AND IN THE BIBLIOGRAPHY BELOW.

ANTARCTICA IS NOT THE HEART OF GLOBAL WARMING.

THE RELEVANT BIBLIOGRAPHY

1. Fisher, Andrew T., et al. “High geothermal heat flux measured below the West Antarctic Ice Sheet.” Science advances 1.6 (2015): e1500093. The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m², significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m². The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.
2. Damiani, Theresa M., et al. “Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica.” Earth and Planetary Science Letters 407 (2014): 109-122. Thwaites Glacier has one of the largest glacial catchments in West Antarctica. The future stability of Thwaites Glacier’s catchment is of great concern, as this part of the West Antarctic Ice Sheet has recently been hypothesized to already be en route towards collapse. Although an oceanic trigger is thought to be responsible for current change at the grounding line of Thwaites Glacier, in order to determine the effects of this coastal change further in the interior of the West Antarctic Ice Sheet it is essential to also better constrain basal conditions that control the dynamics of fast glacial flow within the catchment itself. One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. The crustal thickness beneath Thwaites Glacier is an important contributor to regional-scale geothermal heat flux patterns. Crustal structure is an indicator of past tectonic events and hence provides a geophysical proxy for the thermal status of the crust and mantle. Terrain-corrected Bouguer gravity disturbances are used here to estimate depths to the Moho and mid-crustal boundary. The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area’s subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models.
3. Vogel, Stefan W., and Slawek Tulaczyk. “Ice‐dynamical constraints on the existence and impact of subglacial volcanism on West Antarctic Ice Sheet stability.” Geophysical Research Letters 33.23 (2006). Subglacial volcanism in West Antarctica may play a crucial role in the dynamics and stability of the West Antarctic Ice Sheet (WAIS). Evidence supporting the existence of an individual subglacial volcanic center (Mt. Casertz) in the upper catchments of Whillans and Kamb Ice Stream (WIS and KIS), comes from a comparison of ice sheet modeling results with measured ice velocities. Lubrication of an area, which otherwise should be frozen to its bed, is best explained by basal melt water generated in the vicinity of Mt. Casertz. The estimated melt water production of Mt. Casertz corresponds to ∼8 % of the total melt water production in the two catchments. This would be sufficient to offset basal freezing in the dormant KIS, relubricating its bed and potentially causing a restart. Near future volcanic activity changes are speculative, but would have far reaching implications on the dynamics and stability of the WAIS requiring further investigation.
4. Corr, Hugh FJ, and David G. Vaughan. “A recent volcanic eruption beneath the West Antarctic ice sheet.” Nature Geoscience 1.2 (2008): 122-125. Indirect evidence suggests that volcanic activity occurring beneath the West Antarctic ice sheet influences ice flow and sheet stability. However, only volcanoes that protrude through the ice sheet and those inferred from geophysical techniques have been mapped so far. Here we analyse radar data from the Hudson Mountains, West Antarctica, that contain reflections from within the ice that had previously been interpreted erroneously as the ice-sheet bed. We show that the reflections are present within an elliptical area of about 23,000 km² that contains tephra from an explosive volcanic eruption. The tephra layer is thickest at a subglacial topographic high, which we term the Hudson Mountains Subglacial Volcano. The layer depth dates the eruption at 207 BC±240 years, which matches exceptionally strong but previously unattributed conductivity signals in nearby ice cores. The layer contains 0.019–0.31 km³ of tephra, which implies a volcanic explosive index of 3–4. Production and episodic release of water from the volcano probably affected ice flow at the time of the eruption. Ongoing volcanic heat production may have implications for contemporary ice dynamics in this glacial system.
5. Engelhardt, Hermann. “Ice temperature and high geothermal flux at Siple Dome, West Antarctica, from borehole measurements.” Journal of Glaciology 50.169 (2004): 251-256. A vertical temperature profile through the West Antarctic ice sheet (WAIS) at the summit of Siple Dome reveals an elevated geothermal flux. This could be the root cause for the existence of a dynamic ice-stream system in the WAIS. Siple Dome is still frozen on its bed, but adjacent ice streams have bed temperatures at the pressure-melting point of ice. Although present-day temperature increases due to climatic change do not have an immediate effect on the basal conditions that control the velocity of the ice, indirect effects like a rapid disintegration of the floating ice shelves or additional melt-water input at the surface could give rise to speed-up of the ice streams with an ensuing rise in sea level. Ongoing melt at the base of the ice and changes at the margins will allow continued rapid flow of the ice streams with a possibility of disintegration, within a relatively short period of time, of at least part of the WAIS.
6. Schroeder, Dustin M., et al. “Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet.” Proceedings of the National Academy of Sciences 111.25 (2014): 9070-9072. Thwaites Glacier is one of the West Antarctica’s most prominent, rapidly evolving, and potentially unstable contributors to global sea level rise. Uncertainty in the amount and spatial pattern of geothermal flux and melting beneath this glacier is a major limitation in predicting its future behavior and sea level contribution. In this paper, a combination of radar sounding and subglacial water routing is used to show that large areas at the base of Thwaites Glacier are actively melting in response to geothermal flux consistent with rift-associated magma migration and volcanism. This supports the hypothesis that heterogeneous geothermal flux and local magmatic processes could be critical factors in determining the future behavior of the West Antarctic Ice Sheet.
7. Martos, Yasmina M., et al. “Heat flux distribution of Antarctica unveiled.” Geophysical Research Letters 44.22 (2017): 11-417. Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent‐wide heat flux maps have only been derived from low‐resolution satellite magnetic and seismological data. We present a high‐resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small‐scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high‐resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.
8. Bartolini, Stefania, et al. “Volcanic hazard on Deception Island (South Shetland Islands, Antarctica).” Journal of Volcanology and Geothermal Research 285 (2014): 150-168. Deception Island is the most active volcano in the South Shetland Islands and has been the scene of more than twenty identified eruptions over the past two centuries. In this contribution we present the first comprehensive long-term volcanic hazard assessment for this volcanic island. The research is based on the use of probabilistic methods and statistical techniques to estimate volcanic susceptibility, eruption recurrence and the most likely future eruptive scenarios. We perform a statistical analysis of the time series of past eruptions and the spatial extent of their products, including lava flows, fallout, pyroclastic density currents and lahars. The Bayesian event tree statistical method HASSET is applied to calculate eruption recurrence, while the QVAST tool is used in an analysis of past activity to calculate volcanic susceptibility. On the basis of these calculations, we identify a number of significant scenarios using the GIS-based VORIS 2.0.1 and LAHARZ software and evaluate the potential extent of the main volcanic hazards to be expected on the island. This study represents a step forward in the evaluation of volcanic hazard on Deception Island and the results obtained are potentially useful for long-term emergency planning.
9. Willan, Robert CR, and Debbie C. Armstrong. “Successive geothermal, volcanic-hydrothermal and contact-metasomatic events in Cenozoic volcanic-arc basalts, South Shetland Islands, Antarctica.” Geological Magazine 139.2 (2002): 209-231. Hydrothermal alteration in volcanic arcs occurs in many settings and may involve magmatic, marine, lacustrine or groundwaters, driven by magmatic, tectonic or thermal events. King George Island, part of the South Shetland Island Cenozoic volcanic arc, contains an 80 km long zone of propylitized volcanic rocks, with numerous occurrences of quartz veining, silicic, sericitic, argillic and advanced-argillic alteration. On Barton Peninsula, a basaltic lava sequence (49–44 Ma) intruded by a small, high-level granodiorite pluton (~ 42 Ma), contains these alteration types, previously interpreted as a single porphyry-copper system. In this study, we report three, possibly four, distinct fossil hydrothermal episodes. (1) Banded chalcedonic quartz, quartz-sericite and propylitic alteration occurs along ESE faults and as reworked clasts in nearby tuffs. Drusy quartz + calcite veins with silicic/sericitic, argillic and propylitic wallrocks may represent feeders to the near-surface silicification. These characteristics, and anomalous Ag + Pb + Sb + Au plus Te + Se + Zn + As, suggest a neutral-pH geothermal system that was active during volcanism. (2) The lavas and banded-quartz rocks were brecciated, veined and replaced by alunite + native sulphur + pyrite, and pyrophyllite + quartz + pyrite + zunyite + diaspore assemblages with anomalous Hg + Se + As + Bi + Au + Tl + Sb + Cu. Such advanced-argillic alteration is diagnostic of degassing of a felsic magma into shallow (< 500 m) meteoric groundwaters. Rhyolite tuffs, previously not reported on King George Island, may represent leakage of this magma to the surface. (3) Subsequent burial to ~ 3 km was followed by emplacement of a granodiorite pluton and formation of a silicic contact-metasomatic aureole containing muscovite, biotite, actinolite, magnetite, K-feldspar and tourmaline. Disseminated andalusite + corundum also formed in areas previously affected by the advanced-argillic alteration. Iron/copper-sulphide veinlets are locally abundant, but a porphyry-style geochemical signature is not present. Early Cretaceous Ar–Ar ages near the intrusive contact indicate flow of an excess Ar-bearing hydrothermal plume up the contact. Finally, isolated areas of propylitic alteration in the lavas nearby may be related either to quartz veins of episode 1 at depth or to (4) continued circulation of heated groundwaters around the cooling pluton.
10. Pedrera, Antonio, et al. “The fracture system and the melt emplacement beneath the Deception Island active volcano, South Shetland Islands, Antarctica.” Antarctic Science 24.2 (2012): 173. A new magnetotelluric (MT) survey, along with new topographic parametric sonar (TOPAS) profiles and geological field observations, were carried out on the Deception Island active volcano. 3-D resistivity models reveal an ENE–WSW elongated conductor located at a depth between two and ten kilometres beneath the south-eastern part of the island, which we interpret as a combination of partial melt and hot fluids. The emplacement of the melt in the upper crust occurs along the ENE–WSW oriented, SSE dipping regional normal fault zone, which facilitates melt intrusion at shallower levels with volcanic eruptions and associated seismicity. Most of the onshore and offshore volcanic rocks are deformed by highangle normal and sub-vertical faults with dominant dip-slip kinematics, distributed in sets roughly parallel and orthogonal to the major ENE–WSW regional tectonic trends. Fault development is related to perturbations of the regional stress field associated with magma chamber overpressure and deflation in a regional setting dominated by NW–SE to NNW–SSE extension.
11. Martí, Joan, Adelina Geyer, and Gerardo Aguirre-Diaz. “Origin and evolution of the Deception island caldera (South Shetland Islands, Antarctica).” Bulletin of Volcanology 75.6 (2013): 732. Deception Island has been interpreted as a classical ring fault caldera, as a tectonically controlled collapse caldera or as a tectonic depression. Review of previous studies combined with new fieldwork has allowed us to obtain a more precise model of its formation and internal structure. The Deception Island caldera formed as a result of the explosive eruption of basaltic-to-andesitic magmas, mostly as pyroclastic density currents representing in total a bulk volume of the order of 90 km. Caldera collapse occurred rapidly along a polygonal structural network consisting of several pre-existing major normal faults. These faults, which originated as a result of regional tectonics, controlled pre- and post-caldera volcanism on the island. The formation of the caldera generated a very active geothermal system inside its depression, which is responsible for most of the present-day seismic activity and may also have a significant influence on the observed surface deformation. Our results do not support the hypothesis that there is a large but shallow, active magma chamber beneath the current caldera; instead we suggest that recent eruptions have been fed by small batches of deeper-sourced magmas. The intrusive remains of these eruptions and probably of other minor intrusions that have not reached the surface provide the main heat source that sustains the current geothermal system.