Chile’s Calbuco Volcano Erupts Without Warning. What Can We Expect Next?

Around 5:00 pm local time on April 22, scientists at Southern Andean Volcano Observatory in Chile began picking up volcanic earthquakes at the Calbuco volcano. A disturbingly short 60 minutes later, the volcano was in full eruption, producing an impressive column of ash extending to more than 49,000 feet into the sky. Ash primarily drifted north and northeast of the volcano, covering towns below in a layer of fine ash. Observatory scientists quickly called for an evacuation zone of 12.5 miles

Lava, Ash Flows, Mudslides and Nasty Gases: Good Reasons to Respect Volcanoes

Volcanoes are beautiful and awe-inspiring, but the ongoing eruption of Kilauea on Hawaii’s Big Island is showing how dangerous these events can be. So far this event has destroyed dozens of homes and displaced hundreds of people, but no deaths or serious injuries have been reported. Other volcanic eruptions have had deadlier impacts

Where Were You When the Mountain Blew? Remembering the Eruption of Mount St Helens

May 18, 1980. On that fateful day, Mt St Helens Volcano in Washington exploded violently after two months of intense earthquake activity and intermittent, relatively weak eruptions, causing the worst volcanic disaster in the recorded history of the United States. – US Geological Survey Special Report Without checking your calendar, can you remember where you were on at 8:30 am April 24, 2015? Some of you might, but more will likely have to think hard to remember. In contrast, if you ask someone who lived in the Pacific Northwest 35 years ago where they were at 8:32 am on May 18, 1980, they will tell you exactly what they were doing without hesitatio

Advances in Our Understanding of Pyroclastic Current Behavior from the 1980 Eruption Sequence of Mount St. Helens Volcano (Washington), USA

This review summarizes what the volcanology community has learned thus far from studying the deposits of pyroclastic currents (PCs) from the 1980 eruption sequence at Mount St. Helens. The review includes mass flow events during the May 18 eruption, including the lateral blast, the afternoon column collapse and boil-over PC activity, and some aspects of the debris avalanche. We also include a summary of PCs generated in the smaller eruptions following the climactic May 18 event. Our objective is to summarize the state of our understanding of PC transport and emplacement mechanisms from the combination of field and laboratory observations, granular flow experiments, and numerical modeling techniques. Specifically, we couple deposit characteristics, experiments, and numerical modeling techniques to critically address the problems of (1) constraining conditions in the flow boundary zone at the time of deposition; (2) the influence of substrate roughness and topography on PC behavior; (3) the prevalence, causes, and consequences of substrate erosion by PCs; and (4) the reconstruction of PC transportation and sedimentation processes from a combination of geophysical and sedimentological observations. We conclude by providing opportunities for future research as our field, experimental, and numerical research techniques advance

Active learning through community outreach: A case study of service-learning in a natural hazard, vulnerability and risk class

The popularity of service-learning is increasing, especially at a time where college students want to make a greater impact in their communities. One place we found that students can make a meaningful impact in their communities is promoting community resiliency to natural hazard events through a community outreach project. This article provides a case study of how incorporating service-learning through a community outreach project can increase student engagement, enhance the depth of understanding of a given topic, build communication and teamwork skills, and contribute meaningfully to the students’ community. This article shares how the instructor of a Natural Hazards, Vulnerability and Risk course implement service-learning through a community outreach project, and provides evidence for how such outreach can enhance student learning and address the common problem of student apathy and disengagement. We also discuss the transferability of our approach to other STEM and social science related courses

Estimation of Porosity and Water Saturation in Dual-Porosity Pyroclastic Deposits from Joint Analysis of Compression, Shear, and Electromagnetic Velocities

In situ measurements of porosity and water saturation of pyroclastic deposits have the potential to improve interpretations of geology and hydrology in volcanic regions, and to provide more accurate estimates of dense rock equivalent for volcanic eruptions. However, rock-property models must consider the dual-porosity structure of pyroclastic deposits (i.e., vesicles within pumices and intergranular pores). Vesicularity, intergranular porosity, and water saturation all affect the density, elasticity, and dielectric properties of pyroclastic materials, which control seismic and electromagnetic velocities. The data from active seismic and ground-penetrating radar (GPR) techniques may improve porosity and water saturation estimation if the responses of seismic and electromagnetic velocities to porosity and water saturation variations are complementary in pyroclastic deposits. We developed a dual-porosity petrophysical model to calculate seismic and electromagnetic velocities of pyroclastic deposits with known intergranular porosity, vesicularity, and water saturation, and we tested our ability to estimate porosity and water saturation from field measurements of seismic and electromagnetic velocities in pyroclastic deposits at Mount St. Helens, Washington, USA. Our petrophysical model demonstrates that seismic velocities are more sensitive to intergranular porosity and less sensitive to vesicularity; electromagnetic velocity is primarily controlled by volumetric water content. In a multioffset GPR and active seismic case study, seismic first-arrival traveltime tomography and multichannel analysis of surface waves can resolve high-velocity anomalies caused by porosity reduction. Joint petrophysical inversion of electromagnetic and seismic velocities indicates that although intergranular porosity and water saturation are well-constrained (i.e., standard deviations of approximately 0.05), quantitative estimates of vesicularity remain less certain (i.e., standard deviation of approximately 0.21), due to weak sensitivity

Sequential Fragmentation / Transport Theory, Pyroclast Size-Density Relationships, and the Emplacement Dynamics of Pyroclastic Density Currents – A Case Study on the Mt. St. Helens (USA) 1980 Eruption

Pyroclastic density currents (PDCs) are the most dangerous hazard associated with explosive volcanic eruptions. Despite recent advancements in the general understanding of PDC dynamics, limited direct observation and/or outcrop scarcity often hinder the interpretation of specific transport and depositional processes at many volcanoes. This study explores the potential of sequential fragmentation / transport theory (SFT; cf. Wohletz et al. 1989), a modeling method capable of predicting particle mass distributions based on the physical principles of fragmentation and transport, to retrieve the transport and depositional dynamics of well-characterized PDCs from the size and density distributions of individual components within the deposits. The extensive vertical and lateral exposures through the May 18th, 1980 PDC deposits at Mt. St. Helens (MSH) provide constraints on PDC regimes and flow boundary conditions at specific locations across the depositional area. Application to MSH deposits suggests that SFT parameter distributions can be effectively used to characterize flow boundary conditions and emplacement processes for a variety of PDC lithofacies and deposit locations. Results demonstrate that (1) the SFT approach reflects particle fragmentation and transport mechanisms regardless of variations in initial component distributions, consistent with results from previous studies; (2) SFT analysis reveals changes in particle characteristics that are not directly observable in grain size and fabric data; (3) SFT parameters are more sensitive to regional transport conditions than local (outcrop-scale) depositional processes. The particle processing trends produced using SFT analysis are consistent with the degree of particle processing inferred from lithofacies architectures: for all lithofacies examined in this study, suspension sedimentation products exhibit much better processing than concentrated current deposits. Integrated field observations and SFT results provide evidence for increasing density segregation within the depositional region of the currents away from source, as well as for comparable density-segregation processes acting on lithic concentrations and pumice lenses within the current. These findings further define and reinforce the capability of SFT analysis to complement more conventional PDC study methods, significantly expanding the information gained regarding flow dynamics. Finally, this case study demonstrates that the SFT methodology has the potential to constrain regional flow conditions at volcanoes where outcrop exposures are limited

Does Updating Natural Hazard Maps to Reflect Best Practices Increase Viewer Comprehension of Risk?

In this study, we examine whether updating an interactive hazard map using recommendations from the literature improves user map comprehension. Analyses of experimental data collected from 75 university students revealed that map comprehension scores were not significantly better for those who viewed a “best practices” map compared to those who viewed an existing version. This may be because the existing map was itself better than most other interactive maps. Additionally, we found map comprehension levels to have significant positive relationships with objective tests, but not self-reported measures of spatial ability. Moreover, self-reported spatial ability had statistically significant, but only moderately strong, correlations with objective tests. These results indicate that spatial ability should be measured objectively rather than through self-reported methods in research on map comprehension. Further research is needed to examine the cognitive processes involved in hazard map comprehension, especially using a broader range of map characteristics and population segments with more diverse cognitive abilities

Mafic explosive volcanism at Llaima Volcano: 3D x-ray microtomography reconstruction of pyroclasts to constrain shallow conduit processes

Mafic volcanic activity is dominated by effusive to mildly explosive eruptions. Plinian and ignimbrite-forming mafic eruptions, while rare, are also possible; however, the conditions that promote such explosivity are still being explored. Eruption style is determined by the ability of gas to escape as magma ascends, which tends to be easier in low-viscosity, mafic magmas. If magma permeability is sufficiently high to reduce bubble overpressure during ascent, volatiles may escape from the magma, inhibiting violent explosive activity. In contrast, if the permeability is sufficiently low to retain the gas phase within the magma during ascent, bubble overpressure may drive magma fragmentation. Rapid ascent may induce disequilibrium crystallization, increasing viscosity and affecting the bubble network with consequences for permeability, and hence, explosivity. To explore the conditions that promote strongly explosive mafic volcanism, we combine microlite textural analyses with synchrotron x-ray computed microtomography of 10 pyroclasts from the 12.6 ka mafic Curacautín Ignimbrite (Llaima Volcano, Chile). We quantify microlite crystal size distributions (CSD), microlite number densities, porosity, bubble interconnectivity, bubble number density, and geometrical properties of the porous media to investigate the role of magma degassing processes at mafic explosive eruptions. We use an analytical technique to estimate permeability and tortuosity by combing the Kozeny-Carman relationship, tortuosity factor, and pyroclast vesicle textures. The groundmass of our samples is composed of up to 44% plagioclase microlites, \u3e 85% of which are \u3c 10 µm in length. In addition, we identify two populations of vesicles in our samples: (1) a convoluted interconnected vesicle network produced by extensive coalescence of smaller vesicles (\u3e 99% of pore volume), and (2) a population of very small and completely isolated vesicles (\u3c 1% of porosity). Computed permeability ranges from 3.0 × 10−13 to 6.3 × 10−12 m2, which are lower than the similarly explosive mafic eruptions of Tarawera (1886; New Zealand) and Etna (112 BC; Italy). The combination of our CSDs, microlite number densities, and 3D vesicle textures evidence rapid ascent that induced high disequilibrium conditions, promoting rapid syn-eruptive crystallization of microlites within the shallow conduit. We interpret that microlite crystallization increased viscosity while simultaneously forcing bubbles to deform as they grew together, resulting in the permeable by highly tortuous network of vesicles. Using the bubble number densities for the isolated vesicles (0.1-3−3 × 104 bubbles per mm3), we obtain a minimum average decompression rate of 1.4 MPa/s. Despite the textural evidence that the Curacautín magma reached the percolation threshold, we propose that rapid ascent suppressed outgassing and increased bubble overpressures, leading to explosive fragmentation. Further, using the porosity and permeability of our samples, we estimated that a bubble overpressure \u3e 5 MPa could have been sufficient to fragment the Curacautín magma. Other mafic explosive eruptions report similar disequilibrium conditions induced by rapid ascent rate, implying that syn-eruptive disequilibrium conditions may control the explosivity of mafic eruptions more generally

Dynamic pore-pressure variations induce substrate erosion by pyroclastic flows

International audienceField evidence shows that pyroclastic flows can entrain blocks from underlying substrates formed by earlier geological events, yet, counterintuitively, they are less likely to erode unconsolidated layers of fine particles. Here we report laboratory experiments that reproduce these seemingly contradictory observations and also offer a means to infer pyroclastic flow velocity. Experiments demonstrate that the sliding head of a granular flow generates a dynamic upward pore-pressure gradient at the flow-substrate interface. Associated upward air flux is enough to fluidize a substrate of fines, so that particles are not entrained individually but the substrate instead is subject to small shear instabilities. In contrast, coarse particles forming a non-fluidized substrate are lifted at a critical upward force due to the pore-pressure gradient, according to their individual masses, which provides a basis for a model to calculate the flow velocity. Application to the 18 May 1980 pyroclastic flow deposits at Mount St. Helens (Washington State, USA) gives velocities of ∼9-13 m s-1 at ∼6-7 km from the vent on gentle slopes (<4°-6°), in agreement with field observations at this volcano and at others