Multiple Surges Research Articles

Detecting capital flow surges in developing countries

AbstractThis study investigates excessive movements in capital flows called surges or bonanzas. Contrary to the previous work that extensively uses ad‐hoc measures and discretionary thresholds; we adopt a distinctive methodology to detect capital flow surges based on right‐tailed unit root tests. Generalized supremum augmented Dickey‐Fuller (GSADF) proposed by Phillips et al. (2015) is successfully applied to identify asset price bubbles. Exploiting the technical and conceptual similarities in the formations of asset price bubbles and capital flow surges, we perform the GSADF procedure using quarterly net capital flows data from 43 developing countries. The advantages of this procedure are twofold: it can distinguish the behaviour of volatility and explosiveness and diagnose multiple surges in a series. We identified 727 individual surges, 130 different surge episodes, and 4 global capital flow waves over the periods of 1995–2017. Compared with the existing measures, the application of this surge‐detection technique provides a useful tool as a data‐driven method with no need for discretionary thresholds. We also investigate the factors triggering capital flow surges, employing the Fernandez‐Val and Weidner (2016) bias‐adjusted fixed effects probit model and find that domestic factors play a dominant role on the surge occurrences in developing countries.

Multi-hazard vulnerability of buildings to debris flows

Landslide hazards often occur in succession with multiple hazardous processes. The elements at risk such as buildings are therefore exposed to a multi-hazard environment. Multi-vulnerability assessment is a critical component of multi-hazard risk analysis. In this paper, effect of hazard interactions on the physics of building damage is formulated from the perspective of triggering and temporal relations. A fragility analysis framework for generating physics-based vulnerability models for sequentially and concurrently occurring hazards is proposed. Monte Carlo simulation is used in the framework to include the uncertainties from both hazard intensity and building properties. The framework is illustrated by evaluating the failure probability of a typical reinforced concrete building impacted by multiple surges of debris flows. Considering specific debris flow-building interaction mechanisms, nonlinear finite-element pushover analysis is adopted to obtain the building response under debris flow impact. By quantifying the physical damage caused by the primary debris flow, the cumulative damage effect of the sequentially occurring debris flows is formulated. The amplified damage effect of the concurrently occurring debris flows is however case specific. The proposed methodology shows potential to address more complex multi-hazard scenarios and enhance the multi-vulnerability assessment, filling the research gap on multi-vulnerability assessment for landslide hazards.

Experimental study on impact and deposition behaviours of multiple surges of channelized debris flow on a flexible barrier

Debris flow normally occurs after heavy rains in mountainous regions with multiple surges. Flexible barriers are installed in torrents to intercept debris flows in an early stage. For the safer design of a flexible barrier installed in the upstream, the forces on the barrier invaded by debris flows should be taken into consideration. An outdoor physical modelling facility was utilized to study the interaction between debris flows and a flexible barrier. Three continuous debris flow impact tests were conducted to investigate the performance of a flexible barrier affected and overflowed by multiple surges of debris flow. A parameter named Initial Block Ratio (IBR) is introduced in this study to describe the initial condition of a flexible barrier filled by the earlier debris flow surges. By analysing the results of these tests, the dynamic response of a flexible barrier under the impact of multiple surges of debris flow is studied, and the influence of IBR on the interaction of debris flow with the flexible barrier is investigated. Based on the findings of the experimental study, a new simple method is proposed to calculate the loads on a filled flexible barrier overflowed by debris flow. By comparing with the measured impact force in the overflow test, this method has a good performance and can be utilized in design analysis with further calibration.

Pulse propagation in gravity currents

Real world gravity current flows rarely exist as a single discrete event, but are instead made up of multiple surges. This paper examines the propagation of surges as pulses in gravity currents. Using theoretical shallow-water modeling, we analyze the structure of pulsed flows created by the sequential release of two lock-boxes. The first release creates a gravity current, while the second creates a pulse that eventually propagates to the head of the first current. Two parameters determine the flow structure: the densimetric Froude number at the head of the current, Fr, and a dimensionless time between releases, tre. The shallow-water model enables the flow behavior to be mapped in (Fr, tre) space. Pulse speed depends on three critical characteristic curves: two that derive from the first release and correspond to a wavelike disturbance which reflects between the head of the current and the back of the lock-box and a third that originates from the second release and represents the region of the flow affected by the finite supply of source material. Pulses have non-negative acceleration until they intersect the third characteristic, after which they decelerate. Variations in pulse speed affect energy transfer and dissipation. Critically for lahars, landslides, and avalanches, pulsed flows may change from erosional to depositional, further affecting their dynamics. Gravity current hazard prediction models for such surge-prone flows may underpredict risk if they neglect internal flow dynamics.

Geomorphological evidences of paleosurge activity in Lake Viedma Lobe, Patagonia, Argentina

The valley of Lake Viedma represents one of the main ice flow axes during the Quaternary glaciations of Patagonia. Geomorphological mapping of the eastern sector of the lake, between the shoreline and the end moraine systems attributed to the Last Glaciation, allowed us to recognize a large number of ice-marginal and subglacial landforms. The landform assemblage of this area matches with previous models of surging glacier landsystems around the world. We identified the three geomorphological zones that characterise surging glacier landsystems, with some mixing of the zones, possibly related to multiple surges. The outer zone includes push moraines, thrust-block moraines, overridden moraines and hummocky moraines. In the middle zone, overridden moraines and hummocky moraines were developed. Finally, the inner zone is composed of megaflutes, crevasse-squeeze ridges, eskers and till eskers in a till plain. We interpreted these geomorphological features as evidence of surge activity of the Lake Viedma Lobe. A combination of topographic setting, soft-bedrock and the presence of a proglacial lake in contact with ice could have contributed to the development of surge activity in the Viedma paleoglacier. It could have been triggered by a change in the glacial thermal regime of the Viedma paleoglacier from polar during the Last Glacial Maximum to polythermal or temperate during the beginning of the Late Glacial.

Dynamic effects induced by the impact of debris flows on protection barriers

Debris flow is a transient phenomenon that causes large disasters. Retaining systems, whose design is still nowadays a crucial issue, can mitigate this risk. Multiple surges can arise during this phenomenon; thus, an accurate analysis might consider the impact force time histories rather than only its maxima. The aim of this work is to analyze the effects of the interaction between the debris and the barrier during one surging phenomenon. A discrete element model models the granular motion and the interaction between the debris and a rigid open barrier set at the end of the channel. The estimated interaction force time history is then used as input impact force for the dynamic structural analyses of the piles. A total of 12 different structural sections are adopted and the internal forces at the base are critically compared. It results that the first mode vibration period is the parameter that largely affects the behavior of the piles.

Production and preservation of the smallest drumlins

Few very small drumlins are typically mapped in previously glaciated landscapes, which might be an important signature of subglacial processes or an observational artefact. One hundred and forty-three newly emergent drumlins, recently sculpted by the Múlajökull glacier, have been mapped using high-resolution LiDAR and aerial photographs in addition to field surveying. In this paper, these are used as evidence that few small drumlins (e.g., height H 4 m, width W 40 m, length L 100 m) are produced; at least, few survive to pass outside the ice margin in this actively forming drumlin field. Specifically, the lack of a multitude of small features seen in other landforms (e.g., volcanoes) is argued not to be due to (i) Digital Elevation Model resolution or quality, (ii) mapper ability in complex (i.e., anthropogenically cluttered or vegetated) landscapes or (iii) post-glacial degradation at this site. So, whilst detection ability must still be at least acknowledged in drumlin mapping, and ideally corrected for in quantitative analyses, this observation can now be firmly taken as a constraint upon drumlin formation models (i.e., statistical, conceptual or numerical ice flow). Our preferred explanation for the scarcity of small drumlins, at least at sites similar to Múlajökull (i.e., ice lobes with near-margin drumlin genesis), is that they form stochastically during multiple surge cycles, evolving from wide and gentle pre-existing undulations by increasing rapidly in amplitude before significant streamlining occurs.

Geomorphological investigation of multiphase glacitectonic composite ridge systems in Svalbard

Some surge-type glaciers on the High-Arctic archipelago of Svalbard have large glacitectonic composite ridge systems at their terrestrial margins. These have formed by rapid glacier advance into proglacial sediments during the active surge phase, creating multicrested moraine complexes. Such complexes can be formed during single surge advances or multiple surges to successively less-extensive positions. The few existing studies of composite ridge systems have largely relied on detailed information on internal structure and sedimentology to reconstruct their formation and links to surge processes. However, natural exposures of internal structure are commonly unavailable, and the creation of artificial exposures is often problematic in fragile Arctic environments. To compensate for these issues, we investigate the potential for reconstructing composite ridge system formation based on geomorphological evidence alone, focusing on clear morphostratigraphic relationships between ridges within the moraine complex and relict meltwater channels/outwash fans. Based on mapping at the margins of Finsterwalderbreen (in Van Keulenfjorden) and Grønfjordbreen (in Grønfjorden), we show that relict meltwater channels that breach outer parts of the composite ridge systems are in most cases truncated upstream within the ridge complex by an inner pushed ridge or ridges at their ice-proximal extents. Our interpretation of this relationship is that the entire composite ridge system is unlikely to have formed during the same glacier advance but is instead the product of multiple advances to successively less-extensive positions, whereby younger ridges are emplaced on the ice-proximal side of older ridges. This indicates that the Finsterwalderbreen composite ridge system has been formed by multiple separate advances, consistent with the cyclicity of surges. Being able to identify the frequency and magnitude of former surges is important as it provides insight into the past behaviour of surge-type glaciers and, if absolute dating is possible, allows for the assessment of surge-type glacier response to climate change on decadal to centennial timescales. Although further investigations into the internal structure of these deposits should be sought where possible, our study demonstrates that geomorphology could be an invaluable tool for reconstructing the formation of composite ridge systems.

Large-scale successive boulder impacts on a rigid barrier shielded by gabions

Debris flows occur in multiple surges. Boulders entrained within the flow have been reported to incapacitate structures within its flow path. Single-layer cushions, such as gabions, are often installed to shield debris-resisting barriers from boulder impact. However, most relevant works only focus on single impact and the performance of gabions subjected to successive loading is still not well understood. A new large-scale pendulum facility was established to induce impact energy of up to 70 kJ on an instrumented rigid barrier shielded by 1 m thick gabions. The response of the gabions under six successive impacts was investigated. Results show that the peak boulder impact force given by the Hertz equation is at least four times the measured values. The recommended load-reduction factor (Kc) used in practice can be reduced by a factor of two. After six successive impacts at an energy level of 70 kJ, the transmitted force increases by up to 40%. Based on the Swiss guidelines, a 13% increase of gabion thickness is required when successive impacts are concerned. The results presented in this paper will be useful for practitioners designing rigid barriers.

Seismic analysis of the 13 October 2012 Te Maari, New Zealand, lake breakout lahar: Insights into flow dynamics and the implications on mass flow monitoring

On 6 August 2012 an eruption of the upper Te Maari vent Tongariro volcano and subsequent debris flow in the Mangatetipua channel created a debris dam and ephemeral lake. The lake reached its maximum volume of 50,000m3 by 13 October, initiating dam breaching at 22:30 NZDT (11:30 UTC) after a period of intense rainfall. The breach eventually grew to 29×12m, causing eroded debris flow sediment and water to remobilize as a lahar. The event, comprising multiple surges, lasted ~30min, and displaced 57,000m3 of remobilized sediment up to 4.5km downstream. To determine the dynamics of the event, the seismic signals generated by the lahar were compared with active seismic source data collected in February 2013. The comparison used a common frequency band range of 3–10Hz to compute amplitude for four near-field seismic stations. For periods with signal-to-noise ratios above 2.0, we obtained lahar amplitude distributions that match best the equivalent active source amplitudes within ~0.5km of the dam breakout. The accumulated seismic energy of the lahar was estimated at 1.93×109Nm, whereas the peak energy was 6.88×107Nm. Results of this work may improve the characterization of future mass flow events in the Te Maari/Mangatetipua area through the calibration of seismic stations used in this study.

The evolution of a submarine landform record following recent and multiple surges of Tunabreen glacier, Svalbard

This study focuses on the glacial landform record associated with recent surge events of Tunabreen – a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances.Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.

The effects of recent uplift and volcanism on deposition in Mono Lake, California, from seismic‐reflection (CHIRP) profiles

AbstractAbout 150 km of high‐resolution, seismic reflection (Compressed High‐Intensity Radar Pulse) profiles (approximately 20 m penetration) were collected in Mono Lake in order to define the uppermost sedimentary architecture of the basin, which has been heavily impacted by recent volcanic, tectonic, and climatic processes. The study also provides an important background for ongoing efforts to obtain paleoenvironmental records from sediment cores in the lake. The history of four seismic‐stratigraphic units in the upper 20 m of section are inferred from the data, and the interpretations are generally consistent with previous interpretations of lake history for the past 2000 years, including a major lowstand at 1941 m. No shorelines below the previously documented major lowstand at 1941 m were found. A relatively steep slope segment, whose toe is at about 1918 m, and which occurs on the southern and western margins of the deep basin of the lake, is interpreted as the relict foreset slope of deposition from prograding western tributaries. This topography is unconformably overlain by a unit of interbedded tephra and lake sediments of variable lithology, which contains tephra of the North Mono (600–625 cal yr BP) eruption in its upper part. The tephra‐rich unit is overlain by a mostly massive mudflow deposit that is locally more than 18 m thick and that is distributed in a radial pattern around Paoha Island. The evidence suggests that within the past few hundred years, rapid uplift of Paoha Island through thick, preexisting lake deposits led to widespread slope failures, which created a terrain of disrupted, intact blocks near the island, and a thick, fluid mudflow beyond. As is common in mudflows, the mudflow moved up the depositional slope of the lake floor, terminating against the preexisting slopes, likely in multiple surges. Since about 1700 Common Era, fine‐grained, well‐laminated sediments have accumulated in the deep parts of the lake at anomalously rapid rates, probably driven by continued rapid, small‐scale shedding of sediment from Paoha Island.

The Eyjabakkajökull glacial landsystem, Iceland: Geomorphic impact of multiple surges

A new glacial geomorphological map of the Eyjabakkajökull forefield in Iceland is presented. The map covers c. 60km2 and is based on high-resolution aerial photographs recorded in August 2008 as well as field checking. Landforms are manually registered in a geographical information system (ArcGIS) based on inspection of orthorectified imagery and digital elevation models of the area. We mapped subglacially streamlined landforms such as flutes and drumlins on the till plain, supraglacial landforms such as ice-cored moraine, pitted outwash, and concertina eskers, and ice-marginal landforms such as the large, multi-crested 1890 surge end moraine and smaller single-crested end moraines. The glaciofluvial landforms are represented by outwash plains, minor outwash fans, and sinuous eskers. Extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock. Eyjabakkajökull has behaved as a surge-type glacier for 2200years; hence, the mapped landforms originate from multiple surges. Landforms such as large glaciotectonic end moraines, hummocky moraine, long flutes, crevasse-fill ridges, and concertina eskers are characteristic for surge-type glaciers. The surging glacier landsystem of Eyjabakkajökull serves as a modern analog to the landsystems of terrestrial paleo-ice streams.

Hurricane Flood Protection in NYC—Now Is Not the Time for Multiple Surge Barriers. Discussion of: Hill, D., 2012. The Lessons of Katrina, Learned and Unlearned.Journal of Coastal Research,28(2), 324–331.

The article by Douglas Hill (2012) advocates the building of multiple storm barriers across New York Harbor to control storm and hurricane flooding. He includes a detailed critique of the New York City Panel on Climatic Change (NPCC) report based on their ‘‘dismissal’’ of the storm surge barrier concept. He suggests (p. 328) that the topic was overlooked ‘‘because of the makeup of the NPCC’’ (the absence of civil engineers). He then comments on the possibility of hurricane strikes on New York City (NYC) and their consequences His article has several major problems with omission of the consequences of building the barriers, alternative measures to limit flooding damage, and the most serious is his description of the consequences of a hurricane strike on New York City. The readers of this journal should realize that ‘‘editorials’’ are not fact-checked or peer-reviewed. My purpose in writing this discussion is to correct misperceptions and incorrect inferences, based on my research in this area. I first warned New York City Officials about the consequences of a major hurricane strike hitting New York in the mid-1990s. Since that time, I have been an advisor to both the NYC and NYS Emergency Management Orzanizations and have given hurricane seminars for all the counties in southern New York. I have also researched the hurricane damage potential in the State of New Jersey (Coch, 1999a). My conclusions have been presented in many media presentations and in numerous publications. Douglas Hill has totally ignored these research findings and has not followed proper attribution standards in not citing those works. He has mixed up and given inaccurate data about past hurricanes hitting New York City. His actions will cause needless worry to New Yorkers as he has ignored the progress made in handling hurricane emergencies in the past few years. A notable example of improved emergency management is how the City of New York handled Hurricane Irene in 2011. Any discussion about surge barriers in New York Harbor must consider the oceanographic conditions, and not just the water levels, there. I have spent 30 years studying the Hudson River from Albany to Sandy Hook. Published studies, and studies being completed now, show that water movements in the Upper and Lower Bays of New York Harbor are very complex (Coch, 1987). Water quality and sediment patterns are controlled by complex tidal flows, including net nontidal drift, flow separation, and flow segregation. Understanding these tidal complexities is vital in evaluating the consequences of building these barriers in New York Harbor.

Evolution of a natural debris flow: In situ measurements of flow dynamics, video imagery, and terrestrial laser scanning

Many theoretical and laboratory studies have been undertaken to understand debris-flow processes and their associated hazards. However, complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited. We used a novel combination of in situ measurements of debris-flow dynamics, video imagery, and pre- and postflow 2-cm-resolution digital terrain models to study a natural debris-flow event. Our field data constrain the initial and final reach morphology and key flow dynamics. The observed event consisted of multiple surges, each with clear variation of flow properties along the length of the surge. Steep, highly resistant, surge fronts of coarse-grained material without measurable pore-fluid pressure were pushed along by relatively fine-grained and water-rich tails that had a wide range of pore-fluid pressures (some two times greater than hydrostatic). Surges with larger nonequilibrium pore-fluid pressures had longer travel distances. A wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop. Progressive vertical accretion of multiple surges generated the total thickness of mapped debris-flow deposits; nevertheless, deposits had massive, vertically unstratified sedimentological textures.

Imaging glacial sediment inclusions in 3‐D using ground‐penetrating radar at Kongsvegen, Svalbard

AbstractThe quiescent‐phase surge‐type glacier, Kongsvegen, flows confluent with the continuously fast‐flowing Kronebreen in northwestern Spitsbergen. The lower regions of Kongsvegen overlie glaciomarine sediments, which have been incorporated into the ice during multiple surge events. The resulting englacial structures are exposed at the surface and on a cliff section. These structures have variously been interpreted as thrusts, formed by compression, or sediment‐filled crevasses, formed by extension. We collected a grid of closely spaced ground‐penetrating radar profiles in the area adjacent to the cliff section. Several structures were imaged in 3‐D, including a strong subhorizontal basal reflector, which was underlain by a second, weaker subhorizontal reflector. The basal reflector was occasionally reverse faulted, suggesting compression. Clear englacial features extended upwards from it, dipping up‐glacier at angles of <40° and steepening towards the glacier surface; they had complex geometries that changed rapidly cross‐glacier. The structures were orientated at ∼30° to ice flow, suggesting modification by lateral compression from Kronebreen. Some of these englacial structures clearly crossed the basal reflector. We conclude that the englacial features imaged are not likely to be derived from crevasse filling and were probably formed by thrusting. The results contribute to our understanding of surge initiation and termination processes, and interpretation of features in the palaeorecord. Copyright © 2009 John Wiley & Sons, Ltd.

A debris-flow alarm system for the Alpine Illgraben catchment: design and performance

We describe the development, implementation, and first analyses of the performance of a debris-flow warning system for the Illgraben catchment and debris fan area. The Illgraben catchment (9.5 km2), located in the Canton of Valais, Switzerland, in the Rhone River valley, is characterized by frequent and voluminous sediment transport and debris-flow activity, and is one of the most active debris-flow catchments in the Alps. It is the site of an instrumented debris-flow observation station in operation since the year 2000. The residents in Susten (municipality Leuk), tourists, and other land users, are exposed to a significant hazard. The warning system consists of four modules: community organizational planning (hazard awareness and preparedness), event detection and alerting, geomorphic catchment observation, and applied research to facilitate the development of an early warning system based on weather forecasting. The system presently provides automated alert signals near the active channel prior to (5–15 min) the arrival of a debris flow or flash flood at the uppermost frequently used channel crossing. It is intended to provide data to support decision-making for warning and evacuation, especially when unusually large debris flows are expected to leave the channel near populated areas. First-year results of the detection and alert module in comparison with the data from the independent debris-flow observation station are generally favorable. Twenty automated alerts (alarms) were issued, which triggered flashing lights and sirens at all major footpaths crossing the channel bed, for three debris flows and 16 flood flows. Only one false alarm was issued. The major difficulty we encountered is related to the variability and complexity of the events (e.g., events consisting of multiple surges) and can be largely solved by increasing the duration of the alarm. All of the alarms for hazardous events were produced by storms with a rainfall duration and intensity larger than the threshold for debris-flow activity that was defined in an earlier study, supporting our intention to investigate the use of rainfall forecasts to increase the time available for warning and implementation of active countermeasures.

소결온도가 ZPCCL계 바리스터의 충격전류 스트레스 특성에 미치는 영향

The nonlinear electrical properties and aging characteristics against surge stress of ZPCCL-based varistors were investigated for different sintering temperatures of the range <TEX>$1240-1300^{\circ}C$</TEX>. As the sintering temperature increased, the varistor voltage decreased from 732.2 to 53.8 V/mm, the nonlinear exponent decreased from 58.5 to 4.1, and the leakage current increased from <TEX>$0.38{\mu}A$</TEX> to <TEX>$46.5{\mu}A$</TEX>. The varistors sintered at <TEX>$1250^{\circ}C$</TEX> and <TEX>$1260^{\circ}C$</TEX> exhibited the high stability against multiple surge, <TEX>$150A/cm^2(8{\times}20{\mu}s)$</TEX>. On the whole, the variation rate of electrical characteristics against impulse current stress was gradually increased in order of varistor voltage<TEX>$\rightarrow$</TEX>nonlinear exponent<TEX>$\rightarrow$</TEX>dissipation facto<TEX>$\rightarrow$</TEX>leakage current.

2004 Indian Ocean tsunami inflow and outflow at Phuket, Thailand

At Bangtao Beach, Phuket, the 2004 Indian Ocean tsunami produced a repeated sequence in which rapid inflow of turbulent water was followed by ponding and then by gradual outflow. Photographs and eyewitness accounts show an initial withdrawal followed by series of inflows. The tsunami left behind a sand sheet as much as 25 cm thick that contains parallel, inclined, landward and seaward lamina in addition to the normal grading commonly reported from tsunami deposits. The sheet contains evidence for two times of vigorous inflow. Each of these is marked by mud rip-ups, medium to coarse sand that grades upward to fine, landward-inclined laminae, and a sharp basal contact. The top of the sand sheet, when observed in the first days after the tsunami, abounded in current dune and ripple bedforms of mostly landward orientation. The tsunami's first positive wave left no onshore sedimentary record in this pitting area. The second wave deposited sand that is much less extensive and slightly finer than that of the third wave. The deposit of both these waves contains multiple fining-upward sequences possibly due to multiple surges in one wave train. The depth-averaged flow velocity estimated from thickness and grain size are in the range 7–21 m/s, whereas, a near bottom threshold velocity calculated from bedforms reveals the order of magnitude difference from 1.74 to 1.03 m/s.

Facies variation of eruption units produced by the passage of single pyroclastic surge currents, Hopi Buttes volcanic field, USA

Base surges are a significant volcanic hazard associated with phreatomagmatism, but their transport and depositional dynamics are incompletely understood. Stratigraphic analysis and lateral tracing of surge eruption units produced by the passage of single base surges from Haskie tuff ring, Hopi Buttes volcanic field, USA, extend to > 1 km from the vent and show similar downcurrent changes in lithofacies. Within 200 m of the vent, eruption units are primarily disorganized lapilli-tuff that is rich in juvenile pyroclasts. At distances ≥ 200 m from the vent, eruption units transform into a couplet of juvenile-rich lapilli that grades upward into bedform-bearing ash tuff. At distances ≥ 900 m, upper and lower beds of the eruption unit couplet transform into planar-stratified beds. At distances ≥ 1100 m, couplets composing different eruption units are almost entirely composed of planar beds and amalgamate to form almost identical planar-bedded ash tuff. The collapse of dense eruption columns following explosive magma-wet sediment interaction generated turbulent surge currents. As the surges traveled away from the Haskie vent, they expanded and partitioned into a basal juvenile-rich traction carpet and overlying accidental-rich ash cloud surge. Near the limit of their runout, the surges cooled and lost their pyroclastic load, leaving planar beds of accidental-rich ash. The deposition of multiple surge eruption units with similar lateral and vertical facies transitions and a paucity of interbedded fallout suggests an eruption characterized by recurring phreatomagmatic explosions of similar size and the generation of surges with similar flow characteristics.