University College London

Long period volcanic tremors (LPTs), typically termed as VLP, have been widely observed in many volcanic systems around the world. LPTs in different volcanic settings are often repetitive, suggesting a nondestructive source and providing critical insights into the fluid dynamic processes operating inside a volcanic system. Recently, a deep triggering source of LPT has also been discovered, located between the LPT source and the magma chamber. These diverse and rich signals not only help monitor the state of shallow volcanic conduit and its link to upcoming eruptions. it also helps understand causal triggering of LPT and potentially intra-crustal transport of magma. Given diverse and rich signals within the Aso volcanic system, we further explore other possible sources in the tidal period. We analysed continuous data recorded at two borehole tiltmeters installed at Aso volcano, during the period of 2011-2016. We first perform a polarisation analysis of the ground tilt, filtering in the frequency bands matching the medium-long period tidal constituents, Mm, Mf and S1. The results evidence a well-defined direction of the tilting plane at both sites, with minor fluctuations occurring in 2012 and 2014. Moreover, we investigated the tilt time series the 1-8 hour band. There is a clear variation in azimuth orientation in at least one of the two tiltmeters and these azimuthal variations occur roughly from September 2013 at least until November 2014. In the meantime, LPTs were strong and more active, ash eruption occurred at the end of August 2014, followed by a major Strombolian eruption episode starting at the end of November 2014. In this time interval between September 2013 and November 2014, we further discovered a sequence of nearly monochromatic signals, with repetitive waveforms, a typical period of about 2 hours and a duration of about 9 hours. We extracted these signals and will compare their timing against the LPT catalog we constructed previously. Moreover, we will perform waveform correlation in order to quantify the degree of similarity among these monochromatic signals. Finally, we will attempt to reconcile all these observations in terms of the volcano dynamics and of its different eruptive styles during the 2011-2016 eruption cycle.

Geo-resources are widely exploited in our society, with huge benefits for both economy and communities. Nevertheless, with benefits come risks and impacts. Understanding how such risks and impacts are intrinsically borne in a given project is of critical importance for both industry and society. In particular, it is crucial to distinguish between the specific impacts related to exploiting a given energy resource and those shared with the exploitation of other energy resources. A variety of different approaches can be used to identify and assess such risks and impacts. In particular, Life Cycle Assessment (LCA) and risk assessments (RAs) are the most commonly adopted. Although both are widely used to support decision making in environmental management, they are rarely used in combination perhaps because they have been developed by largely different groups of specialists. By analyzing the structure and the ratio of the two tools, we have developed an approach for combining and harmonizing LCA and MRA; the resulting protocol envisages building MRA upon LCA both qualitatively and quantitatively. We demonstrate the approach in a case study using a virtual site (based on a real one) for geothermal energy production

Ground deformation in volcanic areas induced by geothermal fluid circulation can reveal useful information about the dynamical processes occurring in the subsurface hydrothermal system. In the present work, we investigate tiltmeter time-series recorded at Aso Volcano during 2011–2016, a time interval during which different phases of volcanic activity occurred. We performed polarization analysis of the data and identified peculiar long-lasting (hours) transients, defined as Very-Long-period Tilt Pulses. The transients were further characterized in terms of waveform cross-correlation, particle tilt pattern, energy, and time distributions. The analyses indicate that such signals, which appear like deflation–inflation (DI) events, are associated with a Poissonian process whose underlying dynamics evolves over time always driven by a Poissonian mechanism. The obtained results have been interpreted in light of the available geophysical, geochemical and volcanological information. In this framework, the Very-Long-period Tilt Pulses may be ascribed to the depressurization/pressurization of the shallow hydrothermal system according to a fault-valve mechanism, which was active with different efficiency throughout eruptive and inter-eruptive phases.