Topographic controls on pyroclastic density current dynamics: Insight from 18 May 1980 deposits at Mount St. Helens, Washington (USA)

Brand, Brittany D.; Bendana, S.; Self, Stephen; Pollock, Nicholas

doi:10.1016/j.jvolgeores.2016.04.018

Cited by 28 publications

(28 citation statements)

References 68 publications

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“…It follows that the deposition time takes its maximum value at this percentile (~1250 s, corresponding to 21 min) and ranges from few to 21 min, values that are compatible with other pyroclastic flows that were directly observed (e.g., Brand et al 2016). The deposition time corresponds to the time in which volcanic ash is in the air settling from the turbulent basal part and the co-ignimbrite ash cloud in the waning stage and can be potentially inhaled by human beings and animals.…”

Section: Pollena Vs26-1supporting

confidence: 76%

PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data

Dioguardi

Mele

2018

Bull Volcanol

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This paper presents PYFLOW_2.0, a hazard tool for the calculation of the impact parameters of dilute pyroclastic density currents (DPDCs). DPDCs represent the dilute turbulent type of gravity flows that occur during explosive volcanic eruptions; their hazard is the result of their mobility and the capability to laterally impact buildings and infrastructures and to transport variable amounts of volcanic ash along the path. Starting from data coming from the analysis of deposits formed by DPDCs, PYFLOW_2.0 calculates the flow properties (e.g., velocity, bulk density, thickness) and impact parameters (dynamic pressure, deposition time) at the location of the sampled outcrop. Given the inherent uncertainties related to sampling, laboratory analyses, and modeling assumptions, the program provides ranges of variations and probability density functions of the impact parameters rather than single specific values; from these functions, the user can interrogate the program to obtain the value of the computed impact parameter at any specified exceedance probability. In this paper, the sedimentological models implemented in PYFLOW_2.0 are presented, program functionalities are briefly introduced, and two application examples are discussed so as to show the capabilities of the software in quantifying the impact of the analyzed DPDCs in terms of dynamic pressure, volcanic ash concentration, and residence time in the atmosphere. The software and user's manual are made available as a downloadable electronic supplement.

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Section: Pollena Vs26-1supporting

confidence: 76%

PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data

Dioguardi

Mele

2018

Bull Volcanol

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“…Fluidized and dry granular flow experiments demonstrate that erosion can be aided by vertical pore pressure gradients [Roche et al, 2013] and/or by shear at the flow base [Rowley et al, 2011]. Field observations suggest that erosive capacity is also affected by topographic conditions that increase shear or collisional stresses including the following: (1) propagation on steep slopes close to the substrate's angle of repose (>25 ∘ ) [Cole et al, 1998;Bernard et al, 2014;Brand et al, 2016]; (2) transitions from high to low slope [Scarpati and Perrotta, 2012]; (3) irregular topography, such as debris avalanche hummocks ; or (4) channelized terrains, such as gullies along the flanks of volcanoes [Sparks et al, 1997;Cole et al, 1998].…”

Section: Discussionmentioning

confidence: 99%

Evidence of erosional self‐channelization of pyroclastic density currents revealed by ground‐penetrating radar imaging at Mount St. Helens, Washington (USA)

Gase

Brand

Bradford

2017

Geophysical Research Letters

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The causes and effects of erosion are among the least understood aspects of pyroclastic density current (PDC) dynamics. Evidence is especially limited for erosional self‐channelization, a process whereby PDCs erode a channel that confines the body of the eroding flow or subsequent flows. We use ground‐penetrating radar imaging to trace a large PDC scour and fill from outcrop to its point of inception and discover a second, larger PDC scour and fill. The scours are among the largest PDC erosional features on record, at >200 m wide and at least 500 m long; estimated eroded volumes are on the order of 106 m3. The scours are morphologically similar to incipient channels carved by turbidity currents. Erosion may be promoted by a moderate slope (5–15°), substrate pore pressure retention, and pulses of increased flow energy. These findings are the first direct evidence of erosional self‐channelization by PDCs, a phenomenon that may increase flow velocity and runout distance through confinement and substrate erosion.

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“…This is not particularly surprising, as a wide variety of factors may contribute to observed significant lateral and vertical facies changes within the 18 May PDC deposits (Brand et al, 2016(Brand et al, , 2014. MSH14-01 and MSH14-02 are located 300 m apart and are both overlain by a 35-50 cm thick ash layer, followed by a pink, block-rich unit.…”

Section: Geological Interpretationmentioning

confidence: 95%

Assessing New and Old Methods in Paleomagnetic Paleothermometry: A Test Case at Mt. St. Helens, USA

Bowles

Gerzich

Jackson

2018

Geochem Geophys Geosyst

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Paleomagnetic data can be used to estimate deposit temperatures (Tdep) of pyroclastic density currents (PDCs) by finding the laboratory temperature at which a PDC‐associated thermal remanence is removed. Paleomagnetic paleothermometry assumes that (1) blocking (Tb) and unblocking (Tub) temperatures are equivalent, and (2) the blocking spectrum remains constant through time. The first assumption fails for multidomain (MD) grains, and recent evidence shows that the second is violated in many titanomagnetites, where Tc is a strong function of thermal history. Here we assess the extent to which the standard paleomagnetic method may be biased by a changing Tb spectrum, and we explore a new magnetic technique that instead exploits these changes. Using samples from the 1980 PDCs at Mt. St. Helens, we find that standard methods on oriented lithic clasts provide a Tdep range that overlaps with measured temperatures, but is systematically slightly higher. By contrast, juvenile pumice give Tdep_min estimates that greatly exceed lithic estimates and measured temperatures. We attribute this overestimate to (1) depth‐dependent variations in Tc and Tub resulting from thermally activated crystal‐chemical reordering and (2) MD titanomagnetite where Tub > Tb. Stratigraphic variations in Tc are interpreted in terms of Tdep, giving results mostly consistent with measured temperatures and with the lower end of estimates from lithic clasts. This new method allows us to evaluate temporal and spatial variations in Tdep that would not have been possible using standard paleomagnetic techniques in these lithic‐poor deposits. It also provides information on deposits not accessible by surface temperature probes.

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Topographic controls on pyroclastic density current dynamics: Insight from 18 May 1980 deposits at Mount St. Helens, Washington (USA)

Cited by 28 publications

References 68 publications

PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data

PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data

Evidence of erosional self‐channelization of pyroclastic density currents revealed by ground‐penetrating radar imaging at Mount St. Helens, Washington (USA)

Assessing New and Old Methods in Paleomagnetic Paleothermometry: A Test Case at Mt. St. Helens, USA

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