Catastrophic Discharge Research Articles

How Much Safer Are Solid State Cells? - Quantified Failure Analysis of Next-Generation Solid State Cells during Abuse Testing

Solid-state lithium-ion batteries offer a promising solution for electric vehicle energy storage by replacing flammable liquid organic electrolytes with non-flammable solid alternatives, thus significantly enhancing safety levels.1 However, despite this potential, the safety of these batteries remains a subject of debate due to a lack of quantified understanding, and existing standards may not adequately address anticipated failure modes. Consequently, there is a pressing need to characterize and quantify the safety of solid-state cells, considering the unique chemistry of each component. Although solid electrolytes aim to reduce the instances of soft shorts between electrode, one of the major safety concerns in solid-state batteries is the occurrence of internal short circuits (ISCs) under faliure circumstance, which pose significant challenges in terms of durability and safety, particularly in automotive applications. ISCs can lead to rapid and catastrophic discharge of up to 70% of the total cell energy in under 60 seconds, resulting in substantial self-heating and potentially initiating thermal runaway.2 To evaluate the safety of solid-state cells, abuse testing has become a standard practice, involving techniques such as nail penetration, crush testing, accelerating rate calorimetry, and overcharging. These tests expedite ISC occurrences, enabling researchers to gain insights into cell behaviour under extreme conditions and facilitating safety assessments. In this study, we conducted a comprehensive examination by subjecting commercial solid-state cells and Li-ion cells of similar energy to catastrophic failure conditions. In conducting this work, we aim to provide a comparative analysis of the challenges encountered by solid-state cells and to quantify the impact of scale-up on safety and failure events, ranging from cell capacities of 2 Ah to 10’s of Ah, and examining the propagation of failure through battery packs. To achieve this, we utilized a diverse array of abuse testing and characterization techniques, including X-ray CT, SEM, and GCMS. Through this endeavour, we aim to establish a benchmark for solid-state failure analysis and quantification, contributing to the advancement of safer battery technologies.[1] Mauro Pasta et al 2020 J. Phys. Energy 2 032008[2] Hossein Maleki and Jason N. Howard 2009 J. Power Sources. 2 568-574

Evaluating seasonal variation in macronutrient levels and their impact on water quality in urban coastal waters: A case study in nutrient management along the North Colombo coast of Sri Lanka

Macronutrients are vital for sustaining marine food webs and primary production. However, their overabundance through riverine inflows and untreated wastewater discharges causes adverse ecological changes, especially in developing countries, necessitating effective nutrient management for ecosystem preservation. We assessed macronutrient enrichment and dispersion patterns in the north Colombo coast of Sri Lanka, an urban estuary stressed by untreated wastewater discharge from sewer channels and macronutrients from the Kelani River. Maximum concentrations of NO3−−N, total dissolved nitrogen, PO43−−P and total dissolved phosphorus were 0.085, 0.74, 0.70, and 0.79 mg/L, respectively, while the dissolved oxygen levels and temperature ranged from 6.42 to 8.62 mg/L and from 28.1 to 30.8 0C during January 2023. The estuary was a nitrogen-limited ecosystem, with the Kelani River being the primary source of NO3−−N. Although nutrient levels were within water quality guidelines, understanding how pollutants disperse during a catastrophic discharge is crucial for risk management. Simulated dispersion patterns using Delft3D revealed that NO3−−N and other solutes introduced through the Kelani River accumulate near the breakwaters of the Colombo harbor complex during the Northeast monsoon, primarily due to seasonal wave and wind conditions. The accumulation of the limiting nutrient increased the risk of eutrophication and harmful algal blooms by non-indigenous toxic algae species introduced by untreated ballast water disposal. The findings elucidate the critical role of breakwaters in retaining solutes and emphasize the influence of morphological, climatic, and topographical factors on dispersion patterns in coastal ecosystems. The study provides an example for developing countries to integrate cost-effective monitoring technologies and numerical modelling into coastal management, facilitating data-driven decision making for effective environmental management.

Proactive Process Safety Management - Key to the Prevention of Incidents in Industry

Proactive process safety that works requires a thorough approach that takes into account every area of safety. It entails regular review and monitoring of safety performance in order to pinpoint problem areas and guarantee continued safety improvements. Failure to take proactive measures may result in catastrophic events, such as fires, explosions, or chemical discharges, which could have detrimental effects on nearby communities, the environment, and the workforce. Process effectiveness is continuously ensured through proactive safety, which involves processes, procedures, and people. The purpose of this study was to review proactive process safety management as the key to the prevention of catastrophic incidents in industry. The method adopted for this study was the use of selected process safety incidents to illustrate latent conditions and active failures using the Swiss cheese model and to identify the barrier failures that will lead to catastrophic incidents in industry. A large disaster caused by the effects of catastrophic discharges of hazardous, reactive, flammable, or explosive substances can be prevented to a great extent by implementing proactive systems to monitor process safety.

РЕКОНСТРУКЦИЯ НОВОТРОИЦКОГО ВОДОХРАНИЛИЩА В СТАВРОПОЛЬСКОМ КРАЕ

Purpose: checking the headrace canal to the fall no. 1 for diversion capacity in connection with a change in the canal discharge. Due to the increase in the estimated flow for irrigation and watering, it is planned to build a canal from the reservoir to the fall no. 1. The tasks of the hydraulic computation included the determining of the headrace canal parameters for the intended catastrophic water discharge of 375 cubic m/s, the computation was carried out taking into account the non-steady flow in canal. For effective energy extinction in the tail-race of the fall, it is required to make a constructive decision and carry out a justification taking into account the topographic conditions of the structure's operation. It is necessary to resolve the issue of energy extinction in tail-race of the structure. Calculations of the toothed overfall for energy extinction in the tail-race are presented. Materials and methods. A version of the dissipator with an indented wall which allows dissipate energy in the constraint environment effectively and obtain a favorable distribution of velocities in the flow in tail race of the structure was adopted for the computation. A step-by-step computation for determining the diversion capacity of the fall no. 1 was carried out: first, the diversion capacity of the headrace canal was determined at a catastrophic discharge Q = 375 cubic m/s with a subsequent change in its hydraulic parameters, then the computation for dissipating the flow energy in the downstream of the structure are given. Results: the calculations of the jagged sill for damping the energy in the tail-race are presented, the indented wall of the fall is designed and the corresponding depths in the tail-race are calculated. Conclusions: the performed computation of the headrace canal and fall no. 1 made it possible to ensure the passage of a catastrophic flow rate equal to 375 cubic m/s, under set conditions.

Crater-Based Surface Age Dating of Osuga Valles, Mars

Osuga Valles is a Martian outflow channel system possibly carved by catastrophic discharges of groundwater. To improve our understanding of the history of water on Mars, we are using crater-based surface dating to estimate the age of Osuga Valles. Our preliminary results suggest that it began forming approximately 3 billion years ago and has since been shaped by more recent fluvial activity.

Study of the catastrophic discharge phenomenon in a Hall thruster

In a 1350-W Hall-effect thruster, in which a technique for pushing down the magnetic field is implemented, a catastrophic discharge phenomenon is identified by varying the magnetic field strength while keeping all other operating parameters constant. According to experiments, before and after the discharge catastrophe, the plume changes from focusing state to a divergent state, and discharge parameters such as discharge current and thrust exhibit noticeable changes. The divergence half-angle of the plume increases from 22° to 46°. The oscillation amplitude and mean values of the discharge current significantly increase from 0.8 A to 4 A and from 4.6 A to 6.3 A, respectively, while the thrust increases from 89.3 mN to 91 mN. Analysis of the experimental results shows that as the maximum magnetic field of the thruster we developed is in the plume region, the acceleration occurs in the plume region and a large number of Xe2+ ions appear in the plume area, the catastrophic discharge phenomenon observed.

Evidence of flash floods in Precambrian gravel dominated ephemeral river deposits

Fluvial strata at the base of the Whyte Inlet Formation on Baffin Island, to the west of Sikosak Bay, are predominantly boulder and cobble bearing large pebble conglomerates of braided fluvial origin. Local development of narrow sinuous channels, possibly within the thalwegs of an initially braided bedrock confined system, is indicated by the presence of lateral accretion surfaces, some of which host isolated sub-vertically oriented boulders. These larger boulders were probably emplaced during exceptional flood events involving either hyper-concentrated flows or dilute debris flows, with velocities in the order of 2.2m/s. Isolated ridges of boulders and cobbles are perched on the upper parts of lateral accretion surfaces in mixed sandy-gravelly fluvial intervals. These boulder berms developed down stream from channel bends or bedrock constrictions in response to flow expansion during flash floods, with estimated peak discharge of about 1.4m/s. Associated sandstones on lateral accretion surfaces show evidence of deposition under both upper and lower flow conditions. Similar boulder and cobble berms of this type are known from modern ephemeral and highly seasonal fluvial systems in a wide range of climatic settings, and are a clear indication that highly variable to catastrophic discharge events affected the rivers responsible for deposition of these conglomerates.

Devdoraki Glacier, Kazbek: history of studies of natural hazards in XIX and the beginning of XXI centuries

The Devdorak Glacier located on the Eastern slope of Mt. Kazbek is known since the end of the 19th century for its catastrophic ice discharges into the river Terek canyon. The so-called «Kazbek blockages» stopped the river flow, thus leading to formation of a dammed lake. The lake was then broken through by the heavy floods. Evidences of such events are available for 1776, 1785, 1808, 1817, and 1832. Later on, the glacier surges did sometimes occur, but they never reached the river. The blockages interrupted the traffic on the Georgian Military Highway – the basic way across the main ridge of the Caucasus, for long time periods. Investigations of the Devdorak and other Mt. Kazbek glaciers were organized in 1862 and lasted until the end of 19th century. But the scientists could not reach a common consensus in resolving the main issues, i.e. the causes of the «blockages» and possibilities of their soon repetitions. Different hypotheses explaining the ice discharges by either morphology of the glacier and the river valley or by earthquakes were proposed. Some authors insisted on a probability of occurrence of new «blockages». But the mostly widespread opinion was that since all the Kazbek glaciers were in the state of degradation any risk of new «blockages» was absent while this tendency remained. Since the previous disasters, the Devdorak Glacier posed no threat for about two centuries. However in May 2014, a huge downfall of rock and ice suddenly came down on the glacier in its upper zone. As a result a large mass of rock, stones, and mud blocked the Terek river bed again. This event was not related to regime of the glacier itself. Most likely it was a new manifestation of the Mt. Kazbek volcanic activity.

Sources of water for the outflow channels on Mars: Implications of the Late Noachian “icy highlands” model for melting and groundwater recharge on the Tharsis rise

From the Late Noachian period, through the Hesperian, and into the Amazonian periods on Mars, large outflow channels were formed. Many are interpreted to have originated through the catastrophic discharge of groundwater from martian aquifers, involving the release of up to millions of cubic-kilometers of water. Such a mechanism for outflow channel formation requires that martian aquifers were supplied with significant quantities of water some time prior to the discharge events. Typical groundwater recharge occurs due to the infiltration of surficial waters through a permeable substrate down into aquifers. However, some climate models predict an early martian climate dominated by generally “cold and icy” conditions. In this scenario, a globally continuous, impermeable cryosphere prevents infiltration of liquid water (that might be generated at the surface through anomalous heating conditions), leaving the martian aquifers without an apparent source of recharge to supply later outflow channel formation by groundwater discharge. More recent global climate modeling of an early, thicker CO2 martian atmosphere predicts that, when coupled with a full water cycle, the atmosphere of Mars will behave adiabatically causing temperatures to decrease with elevation. The high standing areas of Mars, such as the southern highlands and the Tharsis region, then act as cold traps. This leads to the preferential accumulation of snow and ice, resulting in the formation of regional ice sheets throughout the highlands that characterize the Late Noachian “icy highlands” early Mars climate model (LNIH). We make the initial assumption that the LNIH model is representative of the early Mars climate, and seek to test the model against the presence of the Hesperian and Amazonian outflow channels to determine if it can be consistent. In order to reconcile the LNIH early Mars climate model with the presence of the later outflow channels a groundwater recharge mechanism that can operate under the predicted “cold and icy” conditions is required. We test basal melting of surface snow and ice in response to a regionally elevated geothermal heat flux throughout the Tharsis rise (resulting from widespread volcanic and magmatic activity during the Noachian) as a mechanism that can provide: (1) liquid water generation at the surface of Mars under generally “cold and icy” conditions, and (2) potentially large scale integration of the hydrological system (through thinning or breaching of the cryosphere), allowing for infiltration of meltwater to provide groundwater recharge during the Late Noachian to supply the later formation of outflow channels. We find: (1) Regional scale basal melting of LNIH ice sheets is not likely to occur at the predicted nominal average ice sheet thicknesses, even in the presence of the anomalous bottom-up heating conditions expected in the Tharsis region (although the increased baseline heating will render the LNIH ice sheets more susceptible to melting through additional anomalous heating conditions introduced by top-down and bottom-up processes). (2) Local scale basal melting and groundwater recharge through a “heat-pipe drain pipe” mechanism is likely to occur, but is not predicted to produce sufficient groundwater recharge to supply the water needed to form the outflow channels. (3) Under the assumption of an ice saturated cryosphere, regional scale melting of the cryosphere due to the insulating effect of the LNIH ice sheets does not provide enough water to explain the formation of all of the outflow channels. Therefore, if the LNIH model is correct, the groundwater recharge that supplied outflow channel formation requires a source that operated earlier in martian history, or the recharge was supplied by other mechanisms.

Experimental study on the triggering mechanisms and kinematic properties of large debris flows in Wenjia Gully

Debris flows are typically caused by natural terrain landslides triggered by intense rainfalls. If an incoming mountain torrent flows along sloping channels at high velocity, huge amounts of sediment (from landslide dams and eroded channel beds) will be entrained into the flows to form debris flows. It is likely that large debris flows are due to the failure of many landslide dams of different scales (due to bank slides or collapses), bed erosion, and solid transport. The catastrophic debris flows that occurred in Wenjia Gully (Wenchuan Earthquake Area), China on August 13, 2010 (two years after the mega earthquake), were caused by intense rainfall and the serious erosion of sloping channels. In the wake of the incident, experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows. The results show that the bed erosion, bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the Wenjia Gully event. This study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream, and how such a complex cascade of geomorphic events (failure of landslide dams and erosion of the sloping bed) can lead to catastrophic discharges. Neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost.

Scale amplification of natural debris flows caused by cascading landslide dam failures

Debris flows are typically caused by natural terrain landslides triggered by intense rainfalls. If an incoming mountain torrent collapses a series of landslide dams, large debris flows can form in a very short period. Moreover, the torrent can amplify the scale of the debris flow in the flow direction. The catastrophic debris flows that occurred in Zhouqu, China, on 8 August 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies. In the wake of the incident, a field study was conducted to better understand the process of cascading landslide dam failures and the formation of debris flows. This paper looks at the geomorphic properties of the debris-flow gullies, estimates the peak flow discharges at different locations using three different methods, and analyzes the key modes (i.e., different landslide dam types and their combinations) of cascading landslide dam failures and their effect on the scale amplification of debris flows. The results show that five key modes in Luojiayu gully and two modes in Sanyanyu gully accounted for the scale amplification of downstream debris flows in the Zhouqu event. This study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream as a complex cascade of geomorphic events (failure of landslide dams and erosion of the sloping bed) can scale to become catastrophic discharges. Neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in a high cost.

Comment on Shaw J., Pugin, A. and Young, R. (2008): “A meltwater origin for Antarctic shelf bedforms with special attention to megalineations”, Geomorphology 102, 364–375

The submarine glacial geomorphology and sedimentology of the cross-shelf troughs and the adjacent continental slope around the Antarctic Peninsula and West Antarctica have been the focus of a series of marine geophysical and geological investigations over the last decade (e.g., [Shipp et al., 1999], [Canals et al., 2000], [Wellner et al., 2001], [Lowe and Anderson, 2002], [O Cofaigh et al., 2002], [Dowdeswell et al., 2004], [Heroy and Anderson, 2005], [Evans et al., 2005], [Domack et al., 2006], [Mosola and Anderson, 2006], [Wellner et al., 2006], [Dowdeswell et al., 2006], [O Cofaigh et al., 2007], O Cofaigh et al., 2008 C. O Cofaigh, J.A. Dowdeswell, J. Evans and R.D. Larter, Geological constraints on Antarctic palaeo-ice stream retreat, Earth Surface Processes and Landforms 33 (2008), pp. 513–525.[O Cofaigh et al., 2008] and [Dowdeswell et al., 2008]). These studies have interpreted sets of characteristic streamlined glacial bedforms and sediments on the shelf, which in numerous cases occur in front of modern ice streams, as largely the product of fast-flowing palaeo-ice streams that drained across the shelf during or following the last glacial maximum. A key feature of these studies is the observation of highly attenuated bedforms known as mega-scale glacial lineations (MSGL), formed in soft sediment on the outer continental shelf. These lineations are regarded as key evidence for streaming flow. In their recent paper, Shaw et al. present a radically different interpretation of the glacial geomorphology of Antarctic cross-shelf troughs in terms of catastrophic discharge of subglacial meltwater floods across the shelf. In their interpretation, MSGL are regarded as the product of erosion by turbulent meltwater flow. The following comment discusses a number of the key assertions made in their paper.

The Lake Superior varve stratigraphy and implications for eastern Lake Agassiz outflow from 10,700 to 8900 cal ybp (9.5–8.0 14C ka)

Glaciolacustrine rhythmites within sediment cores from Lake Superior record the regional recession of the Laurentide Ice Sheet (LIS) from 10,700 to 8900 cal ybp [ca. 9.5–8.0 14C ka]. LIS retreat from Superior opened eastern Lake Agassiz outlets so that the rhythmites reflect the combined impacts of sediment-laden meltwater and Lake Agassiz discharge. Multiple rhythmite stratigraphies, a time series analysis of the thickness measurements, and high-resolution inorganic carbonate data demonstrate that this is an annual record (varved). The varve thickness records primarily document regional ice margin dynamics; correlative thick varve sequences at 9100 cal ybp [∼ 8.1 14C ka] and 10,400–10,200 cal ybp [∼ 9.2–9.0 14C ka] record two periods of enhanced glaciofluvial discharge, most likely moraine formation (the Nakina and Nipigon). General varve cessation is associated with the circumvention of Lake Agassiz and glacial meltwater into Lake Ojibway at 9040 cal ybp [∼ 8.1 14C ka], although adjacent to the inlets from Lake Nipigon, rhythmic sedimentation persisted for 200 years. Positively identifying Lake Agassiz catastrophic discharge events remains speculative but seems feasible. Following retreat of Marquette ice that had re-advanced to fill the basin, the initial influx of Lake Agassiz water is expected at around 10,600 cal ybp [∼ 9.4 14C ka], but at this time, most of northeastern Lake Superior was covered by ice. Three sets of thick–thin varves in western Lake Superior perhaps record influxes of Lake Agassiz at around 10,630, 10,600, and 10,570 cal ybp [∼ 9.4 14C ka]. Varve formation in Superior coincides with high lake levels in Lake Huron, suggesting that high lake levels in Huron correspond to periods of high Agassiz and/or meltwater flow into Lake Superior.

Accelerated drawdown of meridional overturning in the late‐glacial Atlantic triggered by transient pre‐H event freshwater perturbation

Abrupt decreases of the Atlantic meridional overturning circulation (MOC) during the Late Pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater, triggering disruption of northward marine heat transport and causing global climate changes. Here we provide measurements of excess sedimentary 231Pa/230Th from a high‐accumulation sediment drift deposit in the NE Atlantic that record a sequence of sudden variations in the rate of MOC, associated deep ocean ventilation and surface‐ocean climatology. The data series reveal a sequential decrease in the MOC rate at ∼18.0 ka BP ago that coincides with only transient and localized freshwater inputs. This change represents a substantial, though not total, cessation in MOC that predates the major Heinrich (H1) meltwater event by at least 1,200 years. These results highlight the potential of targeted freshwater perturbations in promoting substantial MOC changes without a direct linking with catastrophic freshwater surges.

THE ENVIRONMENTAL RISKS OF TOWING DAMAGED VESSELS: A REVIEW OF PAST CASES

ABSTRACT When a damaged vessel is leaking oil and there is significant risk of further release, spill responders often consider towing the vessel into a harbor of refuge in order to protect it from rough seas and thus prevent a catastrophic discharge of oil, or out to sea to protect the coastline. This paper reviews three cases on the west coast of North America where vessels were towed out to sea (the Puerto Rican, Nestucca, New Carissa). Using actual spill data and modeled trajectories, the environmental impacts associated with towing are compared to the likely environmental impacts that would have occurred with alternative scenaríos. We conclude that, in at least two of these cases, the environmental impacts may have been magnified as a direct result of towing the vessel. Thus, when towing damaged vessels, the environmental risks and tradeoffs should be carefully evaluated.

Field emission device with back gated structure

Analysis and performance optimization of a back-gated field emission device is provided. The device consists of an anode, electron emitting cathodes and gate electrode that are placed below the cathode (“back gate”). The role of a back gate is to control electron emission from the cathode by changing the voltage on the back gate. The top of the cathode is selectively coated with an electron emissive material/structure that presents better emission properties when compared to the material of the cathode. The role of the cathode geometry, back gate voltage, cathode-gate distance, distance between cathode electrodes, the back gate dielectric, as well as field emission characteristics of the emitting material on the top of a cathode were analyzed using continuum electrostatic simulations. The proposed design significantly facilitates fabrication of the field emitting devices while decreasing the amount of charge lost to the gate and potentially reducing the likelihood of catastrophic discharges.

Widely tunable torsional optical filter

A broad range tunable optical filter using a torsional micromechanical structure is presented. The device has a continuous tuning range over 100 nm, from 1500 to 1600 nm, and the structure eliminates the potential catastrophic discharge problem associated with electrostatic micromachines. Transmission of a 2.5-Gb/s directly modulated 1550-nm vertical-cavity surface-emitting laser through the tunable filter shows no power penalty.

Early Holocene change in atmospheric circulation in the Northern Great Plains: an upstream view of the 8.2 ka cold event

Elk Lake, in northwestern Minnesota, contains numerous proxy records of climatic and environmental change contained in varved sediments with annual resolution for the last 10,000 years. These proxies show that about 8200 calendar years ago (8.2 cal. ka; 7300 radiocarbon years) Elk Lake went from a well-stratified lake that was wind-protected in a boreal forest to a well-mixed lake in open prairie savanna receiving northwesterly wind-blown dust, probably from the dry floor of Lake Agassiz. This change in climate marks the initiation of the widely recognized mid-Holocene “altithermal” in central North America. The coincidence of this change with the so-called 8.2 cal. ka cold event, recognized in ice-core and other records from the circum-North Atlantic, and thought by some to be caused by catastrophic discharge of freshwater from proglacial lakes Agassiz and Ojibway, suggests that the two “events” might be related. Our interpretation of the Elk Lake proxy records, and of other records from less accurately dated sites, suggests that change in climate over North America was the result of a fundamental change in atmospheric circulation in response to marked changes in the relative proportions of land, water, and, especially, glacial ice in North America during the early Holocene. This change in circulation probably post-dates the final drainage of proglacial lakes along the southern margin of the Laurentide ice sheet, and may have produced a minor perturbation in climate over Greenland that resulted in a brief cold pulse detected in ice cores.

Source and dispersal of jökulhlaup sediments discharged to the sea following the 1996 Vatnajökull eruption

The October 1996 Gjalp eruption beneath Vatnajokull glacier led to one of the largest jokulhlaups (glacial floods) in Iceland in the twentieth century. A catastrophic discharge of meltwater and sediment swept across the Skeidararsandur flood plain to the sea. Tephra from the eruption consists of vesicular sideromelane shards with a basaltic andesite composition (53% SiO 2 , 3% MgO, 0.8% K 2 O). After the flood, sediment samples were collected from the flood plain and off the southeast coast of Iceland, where a major sediment plume had been created by the discharge. Compositions of glass shards from flood-plain and seafloor deposits do not match those of the Gjalp magma. Flood-plain samples consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are characteristic of Grimsvotn volcanic products (∼50% SiO 2 , 5.5% MgO, 0.4% K 2 O). Marine samples collected near the jokulhlaup outflow into the sea also consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are, for the most part, similar to products of the Grimsvotn volcanic center. Distal marine samples have more vesicular sideromelane clasts with compositions that are similar to products of the Katla volcanic center (e.g., 48% SiO 2 , 4.5% MgO, 0.8% K 2 O). Significant deposition to the seafloor was apparently limited to an area just offshore of the Skeidararsandur. There is no indication that juvenile volcanic material from the Gjalp eruption was carried by the 1996 jokulhlaup onto the flood plain or into the ocean. Instead, the jokulhlaup carried primarily older volcaniclastic material eroded by the flood.

The construction of a drainage tunnel as part of glacial lake hazard mitigation at Hualcán, Cordillera Blanca, Peru

Abstract At Hualcán in the Cordillera Blanca is a high-altitude glacier lake dammed by a moraine. Local glaciers regularly produce ice avalanches. In 1988 it was confirmed that the moraine was ice-cored. The rate of melting of the ice was sufficiently fast that, unless mitigation measures had been undertaken rapidly, the moraine would have collapsed. This would have resulted in the inundation downstream of Carhuaz, a town with a population of 25000 people. Following the successful installation of siphons in 1988–89 to reduce the water level by 8 m, it was decided to undertake more permanent engineering works to ensure that the lake could never again pose a threat. It was proposed to construct a 2-m diameter tunnel, 155 m long beneath a rock bar below the moraine dam, to lower the lake level by a further 20 m. This would create sufficient freeboard to contain possible displacement waves. Work on the tunnel was started in May 1993 using compressed air drilling and blasting with hand excavation. The initial tunnel design consisted of a single tunnel drive 135 m long plus a 20-m inclined drive under the lake. A second, near-vertical shaft was constructed for ventilation and access. Had the proposed method of breakthrough from the tunnel to the lake been carried out, it would have resulted in a rockburst leading to the catastrophic discharge of the lake. The tunnel design was changed on site to include three additional inclined drives from the main shaft, reaching the lake at vertical intervals of 5 m. Using this method, the lake level was lowered 20 m safely. The objective of this paper is to describe in detail the geotechnical engineering aspects of the tunnel construction, the reasons for the change in its design, and the results of the mitigation work.