Computer-assisted mapping of pyroclastic surges

A scenario-based volcanic hazard assessment for the Mount Meager Volcanic Complex, British Columbia

The Mount Meager Volcanic Complex (Mount Meager) is a glacier-clad stratovolcanic system in southwestern British Columbia which last erupted over 2400 years ago (VEI 4). While this is Canada's most recent major explosive eruption, most past research on Mount Meager has focused on its numerous and large volume landslides and thus the volcanic hazard characteristics remain understudied. Here we present a suite of scenario-based hazard maps and an assessment addressing a range of potential future explosive eruptions and associated hazards. In order to overcome limited knowledge of the eruptive history, numerical models have been used to simulate the primary syneruptive hazards of concern (dome-collapse pyroclastic density currents, lahars and tephra fallout) largely utilizing eruption parameters from analogous volcanoes, i.e., glacier-clad stratovolcanoes in a subduction zone setting. This study provides a framework for similar volcanic hazard studies where geologic data is limited, funds are minimal, and access is difficult. Furthermore, this sets the stage for recognizing volcanic hazards in the Canadian landscape, providing a resource to prepare for and mitigate potential impacts well in advance of a crisis situation.

Testing a Comprehensive Volcanic Risk Assessment of Tenerife by Volcanic Hazard Simulations and Social Vulnerability Analysis

Volcanic activity remains highly detrimental to populations, property and activities in the range of its products. In order to reduce the impact of volcanic processes and products, it is critically important to conduct comprehensive volcanic risk assessments on volcanically active areas. This study tests a volcanic risk assessment methodology based on numerical simulations of volcanic hazards and quantitative analysis of social vulnerability in the Spanish island of Tenerife, a well-known tourist destination. We first simulated the most likely volcanic hazards in the two eruptive scenarios using the Volcanic Risk Information System (VORIS) tool and then evaluated the vulnerability using a total of 19 socio-economic indicators within the Vulnerability Scoping Diagram (VSD) framework by combining the analytic hierarchy process (AHP) and the entropy method. Our results show good agreement with previous assessments. In two eruptive scenarios, the north and northwest of the island were more exposed to volcanic hazards, and the east registered the highest vulnerability. Overall, the northern municipalities showed the highest volcanic risk in two scenarios. Our test indicates that disaster risk varies greatly across the island, and that risk reduction strategies should be prioritized on the north areas. While refinements to the model will produce more accurate results, the outputs will still be beneficial to the local authorities when designing policies for volcanic risk reduction policies in Tenerife. This study tests a comprehensive volcanic risk assessment for Tenerife, but it also provides a framework that is applicable to other regions threatened by volcanic hazards.

Scenario-Based Pyroclastic Density Current Invasion Maps at Poorly Known Volcanoes: A Case Study from Changbaishan (China/North Korea)

Changbaishan volcano (China/North Korea; last eruption in 1903 AD) was responsible for a Volcanic Explosivity Index (VEI) 7 eruption in 946 AD. Approximately 186,000 people live around Changbaishan and 2,000,000 tourists/year visit the volcano. An unrest occurred between 2002 and 2006. Despite the relevant hazard, the eruptive history is poorly known, a condition common to many volcanoes worldwide. Here, we investigate the extension of the areas potentially affected by pyroclastic density currents (PDCs) in case of future eruptions following a scenario-based approach. We perform energy cone runs referred to four scenarios from columns of height 3, 10, 20 and 30 km at different vents. By using global datasets on PDCs, we produce spatial probability maps of PDCs invasion. Empirical laws between covered areas, PDC travelled distances, and heights of collapse are provided. In scenarios 3 and 4, PDCs expand at distances up to 42 km and 85 km, respectively. In scenarios 1 and 2, PDCs invade the touristic area and few main roads. Severe effects emerge from scenarios 3 and 4 with the interruption of the China–North Korea land and aerial connections and PDC. Our approach may serve as guide for the rapid evaluation of the PDC-related hazard at poorly known volcanoes.

Karymsky volcano eruptive plume properties based on MISR multi-angle imagery, and volcanological implications

Space-based, operational instruments are in unique positions to monitor volcanic activity globally, especially in remote locations or where suborbital observing conditions are hazardous. The Multi-angle Imaging SpectroRadiometer (MISR) provides hyper-stereo imagery, from which the altitude and microphysical properties of suspended atmospheric aerosols can be derived. These capabilities are applied to plumes emitted at Karymsky volcano from 2000 to 2017. Observed plumes from Karymsky were emitted predominantly to an altitude of 2-4 km, with occasional events exceeding 6 km. MISR plume observations were most common when volcanic surface manifestations, such as lava flows, were identified by satellite-based thermal anomaly detection. The analyzed plumes predominantly contained large (1.28 µm effective radius), strongly absorbing particles indicative of ash-rich eruptions. Differences between the retrievals for Karymsky volcano's ash-rich plumes and the sulfur-rich plumes emitted during the 2014-2015 eruption of Holuhraun (Iceland) highlight the ability of MISR to distinguish particle types from such events. Observed plumes ranged from 30 to 220 km in length, and were imaged at a spatial resolution of 1.1 km. Retrieved particle properties display evidence of downwind particle fallout, particle aggregation and chemical evolution. In addition, changes in plume properties retrieved from the remote-sensing observations over time are interpreted in terms of shifts in eruption dynamics within the volcano itself, corroborated to the extent possible with suborbital data. Plumes emitted at Karymsky prior to 2010 display mixed emissions of ash and sulfate particles. After 2010, all plumes contain consistent particle components, indicative of entering an ash-dominated regime. Post-2010 event timing, relative to eruption phase, was found to influence the optical properties of observed plume particles, with light-absorption varying in a consistent sequence as each respective eruption phase progressed.

Probabilistic-numerical assessment of pyroclastic current hazard at Campi Flegrei and Naples city: Multi-VEI scenarios as a tool for "full-scale" risk management

The Campi Flegrei volcanic field (Italy) poses very high risk to the highly urbanized Neapolitan area. Eruptive history was dominated by explosive activity producing pyroclastic currents (hereon PCs; acronym for Pyroclastic Currents) ranging in scale from localized base surges to regional flows. Here we apply probabilistic numerical simulation approaches to produce PC hazard maps, based on a comprehensive spectrum of flow properties and vent locations. These maps are incorporated in a Geographic Information System (GIS) and provide all probable Volcanic Explosivity Index (VEI) scenarios from different source vents in the caldera, relevant for risk management planning. For each VEI scenario, we report the conditional probability for PCs (i.e., the probability for a given area to be affected by the passage of PCs in case of a PC-forming explosive event) and related dynamic pressure. Model results indicate that PCs from VEI<4 events would be confined within the Campi Flegrei caldera, PC propagation being impeded by the northern and eastern caldera walls. Conversely, PCs from VEI 4–5 events could invade a wide area beyond the northern caldera rim, as well as part of the Naples metropolitan area to the east. A major controlling factor of PC dispersal is represented by the location of the vent area. PCs from the potentially largest eruption scenarios (analogous to the ~15 ka, VEI 6 Neapolitan Yellow Tuff or even the ~39 ka, VEI 7 Campanian Ignimbrite extreme event) would affect a large part of the Campanian Plain to the north and the city of Naples to the east. Thus, in case of renewal of eruptive activity at Campi Flegrei, up to 3 million people will be potentially exposed to volcanic hazard, pointing out the urgency of an emergency plan. Considering the present level of uncertainty in forecasting the future eruption type, size and location (essentially based on statistical analysis of previous activity), we suggest that appropriate planning measures should face at least the VEI 5 reference scenario (at least 2 occurrences documented in the last 10 ka).

The Avellino 3780-yr-B.P. catastrophe as a worst-case scenario for a future eruption at Vesuvius

A volcanic catastrophe even more devastating than the famous anno Domini 79 Pompeii eruption occurred during the Old Bronze Age at Vesuvius. The 3780-yr-B.P. Avellino plinian eruption produced an early violent pumice fallout and a late pyroclastic surge sequence that covered the volcano surroundings as far as 25 km away, burying land and villages. Here we present the reconstruction of this prehistoric catastrophe and its impact on the Bronze Age culture in Campania, drawn from an interdisciplinary volcanological and archaeoanthropological study. Evidence shows that a sudden, en masse evacuation of thousands of people occurred at the beginning of the eruption, before the last destructive plinian column collapse. Most of the fugitives likely survived, but the desertification of the total habitat due to the huge eruption size caused a social-demographic collapse and the abandonment of the entire area for centuries. Because an event of this scale is capable of devastating a broad territory that includes the present metropolitan district of Naples, it should be considered as a reference for the worst eruptive scenario at Vesuvius.

The Taupo eruption, New Zealand. II. The Taupo Ignimbrite

The ca. 30 km 3 Taupo ignimbrite was erupted as a climax to the ca. AD 186 Taupo eruption in the central North Island of New Zealand. It was erupted as a single vent-generated flow unit over a time period of ca. 400 s and was emplaced very rapidly (locally at more than 250-300 m s -1 ) and violently. The parent flow reached 8 0 + 10 km from source in all directions, crossed all but one of the mountains within its range and only stopped when it ran out of material. The ignimbrite is divisible into layers 1 and 2, and a distant facies which combines features of both layers. Layer 1 was generated as a result of strong fluidization in the flow head, caused by air ingestion, and consists of two main facies. Layer 1(P) is a pumiceous, mildly to strongly fines-depleted unit, generated by the expulsion of material from the flow front, and termed the jetted deposits. The overlying layer 1 (H) is a thinner, crystal- and lithic-rich, fines-depleted unit, generated by the sedimentation of coarse/dense constituents segregated out by strong fluidization within the flow head and termed the ground layer. Layer 2 consists of two facies with similar compositions but contrasting morphologies; during emplacement, material left behind by the flow body partially drained into depressions to form the valley-ponded ignimbrite, leaving the veneer deposit as a thin, landscape mantling layer on interfluves. The distant facies occurs in some outermost hilly areas of the ignimbrite where the flow velocity remained high but its volume had shrunk through deposition so that air ingestion fluidization affected the whole flow. The ignimbrite shows great lateral variations. Each facies, or variants therein, exhibits systematic degrees of development with varying distances from vent. Near vent, the flow consisted of a series of batches of material which by ca. 25 km had coalesced into a single wavy flow and by ca. 40 km into a single wave. Out to ca. 13 km, the flow was rather dilute and highly turbulent as it deflated from the collapsing eruption column. Beyond this distance it was fairly concentrated, being less than 100% expanded over its non-fluidized compacted state, and had acquired a fluidization-induced stable density stratification, which strongly suppressed turbulence in the flow body. Deflation from the eruption column was largely complete by ca. 13 km but influenced the flow as far as 20-25 km from vent. Grainsize and compositional parameters measured in the ignimbrite show lateral variations which equal or exceed the entire spectrum of published ignimbrite data. The flow had deflated and coalesced from the eruption column by ca. 20 km from vent. Beyond this distance most lateral variations are modelled by considering the flow to be a giant fluidized bed. As the flow moved, material was deposited from its base, and hence predictable vertical variations in the model fluidized bed are comparable with lateral variations in the ignimbrite. The agreement is excellent, and, in particular, discontinuities in the nature of the ignimbrite at 55-60 km from vent suggest that the more distal ignimbrite represents a vast segregation layer generated above the moving flow. Differences between the model and variations of some parameters reflect the influence of kinetic processes, such as shearing and local fluidization, that operated regardless of the bulk flow composition. The strong fluidization in the flow is a result of the high flow velocities (promoting air ingestion), not vice versa as is often accepted. Contrasts in the natures of layers 1 and 2 imply that the first material erupted contained significantly coarser, and a higher content of, lithics than the bulk of the flow. During emplacement, this earlier material was depleted by deposition and diluted by material introduced from the flow body. Systematic regional variations also occur in the ignimbrite: for example, it contains lower crystal: lithic ratios and higher density pumice in a northeasterly sector, and vice versa to the southwest. Ignimbrite found in mountainous areas shows changes consistent with its derivation from the upper, more mobile and pumiceous top of the flow. Fluidization processes generated structures and facies in the ignimbrite on various scales. Individual segregation bodies found at any exposure show features mimicking those of the ground layer, i.e. fines depletion and crystal- and lithic-enrichment. Fluidization-induced grading visible at individual exposures accounts for the great range of grading styles seen in the valley-ponded ignimbrite, and strong fluidization has locally generated an upper fines- and pumice- rich segregation layer (here termed layer 2c). On the largest scale, fluidization was primarily responsible for the generation of the layer 1 deposits, and for the grainsize and compositional zonation within the flow that produced the lateral variations in the ignimbrite. Ingested and heated air is inferred to have been the most important gas source for fluidization within the flow, although several other gas sources were locally dominant. It is clear that the thickness, grainsize and composition of the ignimbrite at any point are not simply related to values of these parameters in either the originally erupted material or the parent flow, and that, except for its density, the dimensions and composition of the parent flow cannot be directly inferred from the ignimbrite.