Volcano-hydrologic hazards associated with the April 2015 eruption of Calbuco volcano, Chile

Volcanoes generate a wide range of hazards across a variety of timescales. In addition to the more familiar primary hazards to life and infrastructure associated with eruptive activity, such as ashfall, pyroclastic density currents (hot gas and particle-charged avalanches) and lava flows, in many cases the secondary hazards that arise from the remobilisation of the loose erupted material by rain and running water after the eruption is over are more devastating, longer-lasting, and reach further afield.

Lahars, gravity-driven flows of volcanic debris and water, are of particular concern due to their rapid onset, mobility, high energy, and ability to impact areas far removed from perceived zones of hazard. Since 1600 AD, lahars have been responsible for 17% of all deaths due to volcanic activity, being triggered either directly by volcanic activity (i.e. by ejection of a crater lake or melting of a summit ice cap by pyroclastic flows) or indirectly as secondary events (i.e. by rainfall remobilisation of fresh pyroclastic deposits or break-outs from volcanically-dammed lakes). However, these phenomena are amongst the most poorly understood of all volcanic hazards because of their complexity and unpredictability, hampering strategies designed to militate against their potential to cause loss or damage. A key to improving our understanding and knowledge of lahars lies in field-based studies that constrain their source conditions and initiation, and how they evolved during downstream flow, picking up and dropping sediment-load along the way and interacting with the channel margins.

The recent eruption of Calbuco volcano on 22-23 April 2015, in the Southern Andes of Chile, offers an opportunity to study lahars as they happen. Calbuco is one of more than 66 known active volcanoes in the southern Andes, an area that hosts 80% of Chile's population. Historic eruptions in the area have been accompanied by multiple eruption- and rain-triggered lahars, causing most the region's eruption-related deaths in the 20th Century. As economic growth in the area continues, an increasing population and infrastructure base is becoming exposed to these hazards, creating an urgent need for better quantification and understanding of such events.

We will undertake fieldwork to map and characterise the deposits of the primary, eruption-triggered hot lahars that occurred during the initial eruptive phase and destroyed bridges and infrastructure in a number of river valleys around the mountain. The eruptions also deposited a thick layer of ash and lapilli on the steep, seasonally snow-clad upper slopes of Calbuco, and the nearby cone of Osorno volcano, priming the region for an intense phase of rain-triggered remobilisation during the impending Southern Hemisphere winter when the region receives most of its annual rainfall. We will measure the properties of the ash deposits in a range of locations and instrument key monitoring sites with time-lapse cameras and rain gauges to enable us to track the response of the ash layer to rain-fall events and their combined role in lahar initiation. Repeat measurements will document the evolution of the ash layer as it degrades and is eroded over time. Further downstream, we will measure the dimensions and geometry of the lahar channels and instrument them with sensors that detect and record the ground-shaking caused by the flow events, enabling us to measure their timing, magnitude, speed, and location. Time-lapse and triggered video cameras will record vital information on flow depth and sediment concentration. This combination of data will permit, for the first time, direct correlations between conditions in lahar source zones and the resulting flows. Remote-sensed satellite data, including high-resolution optical and multispectral imagery and Sentinel-1 X radar interferometry data will be used to map the evolution of lahar paths through time and construct high-resolution digital elevation models.

This project will directly improve the understanding of lahar generation and emplacement mechanisms, providing vital new information on this important class of natural hazard. Results will be recorded and disseminated in a range of formats and methods to maximise uptake and impact. As the timescale of the project is relatively short (12 months) some impacts will be realised after its formal (budgetary) closure.
The project team are already involved in a number of scientific community initiatives, and results will be leveraged through this existing framework. In addition to conference presentations and peer-reviewed articles, dissemination will occur through engagement with two active IAVCEI commissions; the Commission on Hazards and Risk of which Calder is a leader and the Commission on Volcanic Sedimentation (Calder and Manville are members): these groups host conference sessions and hold regular workshops. Furthermore, the 2016 IAVCEI Cities on Volcanoes 9 conference, which attracts scientists, social scientists and government agencies, will be held in Puerto Varas, only 30 km from Calbuco volcano, where we will propose a session on volcano-hydrologic hazards with the aim of attracting contributions which range from understanding the physical processes, to community awareness and risk mitigation.
Project Partner Amigo, at SERNAGEOMIN, the Chilean Government institution responsible for monitoring volcanoes in the southern Andes, will facilitate the channelling of project outcomes through SERNAGEOMIN. Co-I Calder has long-standing links with SERNAGEOMIN including ongoing collaborations with others in the volcanic hazards group. We will organise meetings at SERNAGEOMIN at the beginning of each field trip, to discuss project objectives and logistical arrangements given the state of the volcano, and at the end of trips to share results. These meetings will allow dissemination of project data and findings into policy decisions: SERNAGEOMIN science informs the Chilean Government risk and emergency management agency OMENI, thus, indirectly our project outcomes could affect the medium-to long term management strategy for dealing with persistent lahar production in the area. On the second visit to Chile, the team including project partners will host a two day workshop on lahar hazards in Santiago, Chile. This workshop will involve project partners and other local scientists, and in addition representatives from civil engineering concerns, ONEMI, the Direccion General de Aguas, and NGO's. In addition, we will leverage local community-based efforts already set in place by SERNAGEOMIN. The work proposed here, would inform SERNAGEOMIN plans to build a lahar monitoring network around Calbuco (see Lara - letter of support), which would directly lessen the risk to life in the surrounding area. Although not explicitly part of the project we will contribute any of our outcomes to aid development of such an initiative through project partner Amigo.
To ensure maximum possible utility of our project, data will be made available (after a 2 year embargo period to allow for publications by the project team) to the scientific community through uploading of data and results to a number of on-line databases, including: (i) VHub (VHub.org), a cyber-infrastructure for volcanic hazard collaboration; and ultimately (ii) the NERC National Geoscience Data Centre. In addition, we will utilise server storage at the University of Leeds and the Edinburgh DataShare (http://datashare.is.ed.ac.uk/), a data archiving site operated by the University of Edinburgh for redundancy. Key metadata information (site locations, dates, type of data etc.) will be collected to accompany this data to ensure maximum discoverability by the volcanology community. This project offers an opportunity to energise and grow the UK and international lahar community, in part by developing a community repository of the data needed to calibrate and test numerical models of lahar behaviour