Thomas C. Pierson

• PhD
• Research Hydrologist (retired) at United States Geological Survey

Volcanic and volcaniclastic fragmental deposits can be identified and differentiated through examination of their sediment-body characteristics, the physical properties of their constituent particle mixtures, and any impacts to terrain caused by the processes that emplace them. These identification criteria are observable and measurable at differen...

The distribution of volcanic and volcaniclastic deposits in both space and time gives important clues to their origins. Distance from volcanic source, depositional setting, and stratigraphic associations are important spatial characteristics. Timing of volcanic flows with respect to associated eruptions, as well as timing of flows with respect to e...

Lahars are highly hazardous volcanic wet flows, owing to their potentially large volumes, rapid velocities, long runouts, frequent occurrence during and following eruptions, and unpredictability. However, lahars are not a specific flow type. They are, instead, time-discrete flow events like flash floods, which involve up to three distinct types of...

Floods of water originating from volcanically disturbed landscapes—volcanic water floods (VWFs)—differ from floods in most other types of drainage basins in the world in significant ways. They flow at higher discharges (flow rates), have higher flood peaks, and have shorter flow durations relative to watershed area than most other types of floods....

Deposits of volcanic water floods (VWFs) commonly comprise a significant proportion of the volcanic deposits on the lower edifice flanks and in downstream river valleys at many volcanoes. Following explosive eruptions, the availability of abundant fresh and loose volcaniclastic sediment typically leads to extreme sediment loading in rivers and thic...

Comparison of outcrop photographs is an important additional tool for use in the field to aid in the tasks of deposit differentiation and identification. The collection of outcrop photographs in this chapter provides a basis for visual comparison. Images, mainly of vertical outcrop faces, are presented for all the deposit types described in this bo...

Gravity-driven flows of material emanating from volcanoes during or following eruptions can range from flowing molten rock to flowing denser-than-air volcanic gas. But the bulk of volcanic flows involve two-phase mixtures of solid rock fragments and a fluid—either liquid water or gas composed of air ± volcanic gases. Deposits of the various particl...

Pyroclastic density currents (PDCs), tephra falls (TFs), and glaciers deposit volcanic sediment, including juvenile volcaniclastics, in the same depositional zones as volcanic wet flows—on the flanks of volcanic edifices and in downstream river valleys. These processes can emplace deposits that closely resemble those of volcanic wet flows, and thes...

Volcanic debris avalanches (VDAs) emplace characteristically multicolored, hummocky deposits that are typically coarse, unusually thick, poorly sorted, and contain a wider range of components and sedimentary textures than the deposits of other volcanic wet flows. Debris-avalanche blocks, a component unique to VDA deposits (and to some deposits of l...

Concentrated lahars moving as debris flow are termed volcanic debris flows (VDFs). The unstratified deposits of individual VDFs commonly contain particles ranging from clay size to boulders and may contain blocks 10 m or more in diameter. Deposit volumes can exceed 1 km3. Relatively small amounts of clay-size particles in VDF slurries play importan...

Dilute lahars moving as hyperconcentrated flow are termed volcanic hyperconcentrated flows (VHFs). Their deposits commonly comprise faintly stratified sandy beds with minor gravel lenses and isolated large gravel clasts, but deposit characteristics can vary with solids concentration of the flow. Some dilute lahars flow as VHFs from start to finish,...

Volcanic debris avalanches (VDAs) start as rapid gravitational collapses (landslides) of weakened volcanic edifices, which can vary from limited-volume flank failures that leave relatively shallow scars on volcano sides to enormous edifice-collapse failures involving the volcano summit and core, leaving deep-seated, bowl-shaped, open-sided depressi...

This chapter presents two tools for use in the field to aid in differentiation and identification of volcanic deposits emplaced on dry land: a quick-reference key for deposit identification (Table 1) and a set of tables summarizing all the evaluation criteria for each deposit type, including each type of volcanic wet flow and the three other types...

Lahar, an Indonesian word for volcanic mudflow, is a mixture of water, mud, and volcanic rock flowing swiftly along a channel draining a volcano. Lahars can form during or after eruptions, or even during periods of inactivity. They are among the greatest threats volcanoes pose to people and property. Lahars can occur with little to no warning, and...

Hazards assessments at explosive volcanoes commonly focus on primary phenomena such as debris avalanches, pyroclastic density currents, lahars, and airfall tephra. Although primary processes can be devastating and far reaching, secondary hydrologic and geomorphic (hydrogeomorphic) processes to eruptions-such as flooding; sediment redistribution; an...

The 10 day explosive phase of the 2008-2009 eruption of Chaitén volcano, Chile, draped adjacent watersheds with a few cm to >1 m of tephra. Subsequent lava-dome collapses generated pyroclastic flows that delivered additional sediment. During the waning phase of explosive activity, modest rainfall triggered an extraordinary sediment flush which swif...

Lahars are rapid flows of mud-rock slurries that can occur without warning and catastrophically impact areas more than 100 km downstream of source volcanoes. Strategies to mitigate the potential for damage or loss from lahars fall into four basic categories: (1) avoidance of lahar hazards through land-use planning; (2) modification of lahar hazards...

Explosive eruptions can severely disturb landscapes downwind or downstream of volcanoes by damaging vegetation and depositing large volumes of erodible fragmental material. As a result fluxes of water and sediment in affected drainage basins can increase dramatically. System-disturbing processes associated with explosive eruptions include tephra fa...

Redoubt Volcano in south-central Alaska began erupting on March 15, 2009, and by April 4, 2009, had pro-duced at least 20 explosive events that generated multiple plumes of ash and numerous lahars. The 3108-m-high, snow-and ice-clad stratovolcano has an ice-filled summit crater that is breached to the north. The volcano supports about 4 km 3 of ice...

Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the...

The 10-day explosive phase at the start of the 2008–2009 eruption of Chaitén volcano in southern Chile (42.83°S, 72.65°W) blanketed the steep, rain-forest-cloaked, 77-km2 Chaitén River drainage basin with 3 to >100 cm of tephra; predominantly fine to extremely fine rhyolitic ash fell during the latter half of the explosive phase. Rain falling on th...

Antes de la erupción de mayo de 2008, se pensaba que la última erupción del volcán Chaitén había ocurrido hace más de 5.000 años, lo que sugería un muy largo período de reposo en un segmento de arco volcánico tan activo. Sin embargo, cada vez más erupciones holocenas han sido identificadas. Este artículo presenta evidencia geológica e histórica de...

Dating of many types of young (<500 year), dynamic, geomorphic landforms (e.g. mass-movement erosional tracks and deposits, alluvial terraces, flood plains, etc.) for purposes of hazard assessment and mitigation commonly requires greater dating precision than is available through radiocarbon dating or other methods. Ages of trees growing on landfor...

Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the...

A functional tabletop exercise was run on November 14–15, 2011 in Salt Lake City, Utah, to test crisis response capabilities, communication protocols, and decision-making by the staff of the multi-agency Yellowstone Volcano Observatory (YVO) as they reacted to a hypothetical exercise scenario of accelerating volcanic unrest at the Yellowstone calde...

The Cuttingsville composite stock has feldspathoid-bearing and quartz–bearing alkaline rocks emplaced in Precambrian schists of the Green Mountains. The main intrusions are, from oldest to youngest: (1) hastingsite foyaite and biotite foyaite, (2) diorite, (3) essexite, porphyritic essexite, plagifoyaite, and sodalite foyaite, (4) alkaline quartz s...

A dome-building eruption at Mount Hood, Oregon, starting in A.D. 1781 and lasting until ca. 1793, produced dome-collapse lithic pyroclastic flows that triggered lahars and intermittently fed 108 m3 of coarse volcaniclastic sediment to sediment reservoirs in headwater canyons of the Sandy River. Mobilization of dominantly sandy sediment from these r...

3 GSA Bulletin; January/February 2011; v. 123; no. 1/2; p. 3–20; doi: 10.1130/B30127.1; 10 fi gures; 3 tables. ABSTRACT A dome-building eruption at Mount Hood, Oregon, starting in A.D. 1781 and lasting un-til ca. 1793, produced dome-collapse lithic pyroclastic fl ows that triggered lahars and in-termittently fed 10 8 m 3 of coarse volcaniclastic se...

Explosive activity at Chaitén volcano in May 2008 and subsequent dome collapse nine months later triggered pyroclastic density currents (PDCs) that choked proximal reaches of channels draining the volcano with as much as 10 m of sediment. A north-directed, 1-km-wide, blast-like PDC, probably occurring between 6-12 May, cut a swath about 2 km long t...

The explosive phase of recent activity at Chaitén volcano in southern Chile (42.8° S 72.7° W), a VEI 4-5 eruption on 1-8 May 2008, blanketed large areas of steep forested terrain in a sector NE to SE of the vent with a sequence of tephra layers composed predominantly of fine to coarse, pumiceous ash. Total tephra accumulation in the upper Río Chait...

High-silica rhyolite magma fuels Earth's largest and most explosive eruptions. Recurrence intervals for such highly explosive eruptions are in the 100- to 100,000­year time range, and there have been few direct observations of such eruptions and their immediate impacts. Consequently, there was keen interest within the volcanology community when the...

The spectacular eruption of Mount St. Helens on 18 May 1980 electrified scientists and the public. Photodocumentation of the colossal landslide, directed blast, and ensuing eruption column—which reached as high as 25 kilometers in altitude and lasted for nearly 9 hours—made news worldwide. Reconnaissance of the devastation spurred efforts to unders...

Redoubt Volcano in south-central Alaska began its most recent eruption on March 15 and erupted explosively at least 20 times between then and April 4, 2009. The 3110 m high, snow-and-ice-clad stratovolcano includes a circular, ice-filled summit crater that is breached to the north. The volcano supports about 4 km3 of ice and snow and about 1 km3 of...

This volume contains guides for 33 geological field trips offered in conjunction with the October 2009 GSA Annual Meeting in Portland, Oregon. Showcasing the region’s geological diversity, the peer-reviewed papers included here span topics ranging from accreted terrains and mantle plumes to volcanoes, floods, and vineyard terroir. Locations visited...

Dating of dynamic, young (<500 years) geomorphic landforms, particularly volcanofluvial features, requires higher precision than is possible with radiocarbon dating. Minimum ages of recently created landforms have long been obtained from tree-ring ages of the oldest trees growing on new surfaces. But to estimate the year of landform creation requir...

Within zones of little or no deformation by internal shearing in debris flows at Mt Thomas, about two‐thirds of the weight of large particles is supported by buoyancy and about one‐third by static grain to‐grain contact. In boundary shear zones of low velocity flows and in high velocity, turbulent debris flow, grain‐to grain contact is replaced by...

In the 11 January 2005 issue of Eos , Soroosh Sorooshian offered cogent suggestions about how we, as professional scientists, might do more to make the world safer from natural hazards. Not explicitly mentioned was an additional important contribution we can make that requires no additional research. It is simply to more effectively apply what is a...

P ost-fl ood indirect measurement techniques to back-calculate fl ood magnitude are not valid for debris fl ows, which commonly occur in small steep watersheds during particularly intense rainstorms. This is because debris fl ows can move much faster than fl oods in steep channel reaches and much slower than fl oods in low-gradient reaches. In addi...

Since 1534, Cotopaxi volcano, Ecuador has produced fi ve eruptive periods with numerous vei 3-4 eruptions, all of andesitic affi nity. Due to melting of the glacier cap by pyroclastic fl ows, voluminous lahars formed and fl owed for hundreds of kilometers, passing through the Chillos and the Latacunga Valleys via major drainages. The most distincti...

Geomorphic models are increasingly used to support public policy and natural resources management. We present five examples of the interaction between models and managers and consider factors that influence their success or failure. Essential elements include common objectives for management and models and clear communication of the assumptions, li...

Explosive volcanic eruptions perturb water and sediment fluxes in watersheds; consequently, posteruption sediment yields can exceed pre-eruption yields by several orders of magnitude. Annual suspended-sediment yields following the catastrophic 1980 Mount St. Helens eruption were as much as 500 times greater than typical background level, and they g...

 Travel times for wet volcanic mass flows (debris avalanches and lahars) can be forecast as a function of distance from source when the approximate flow rate (peak discharge near the source) can be estimated beforehand. The near-source flow rate is primarily a function of initial flow volume, which should be possible to estimate to an order of magn...

Lahar hazard at Pinatubo is a function of prodigious sediment yield from Pinatubo's upper and middle slopes and the sediment storage capacity in the adjoining lowlands. Both are diminishing but at mismatched rates. Sediment yields set world records during the first three posteruption years, and yields in the Balin Baquero-Bucao and Marella watershe...

Theoretical modelling is not yet adequate to predict the behavior of debris flows, which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions, particularly at snow-clad stratovolcanoes. To provide a realistic basis for modelling the behavior of large (> 1000 m3/s) debris flows, this paper summarizes kinematic...

A generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at Mount St. Helens, Nevado del Ruiz, and Redoubt Volcano between 1982 and 1989. These "mixed avalanches' traveled as far as 14 km at velocities up to ~27 m/s, involved as much as 107 m3 of rock...

Ice diamict comprising clasts of glacier ice and subordinate rock debris in a matrix of ice (snow) grains, coarse ash, and frozen pore water was deposited during the eruption of Redoubt Volcano on December 15, 1989. Rounded clasts of glacier ice and snowpack are as large as 2.5 m, clasts of Redoubt andesite and basement crystalline rocks reach 1 m,...

The rheology of slurries consisting of less-than-or-equal-to 2-mm sediment from a natural debris flow deposit was measured using a wide-gap concentric-cylinder viscometer. The influence of sediment concentration and size and distribution of grains on the bulk rheological behavior of the slurries was evaluated at concentrations ranging from 0.44 to...

A complex sequence of pyroclastic flows and surges erupted by Nevado del Ruiz volcano on 13 November 1985 interacted with snow and ice on the summit ice cap to trigger catastrophic lahars (volcanic debris flows), which killed more than 23,000 people living at or beyond the base of the volcano. The rapid transfer of heat from the hot eruptive produc...

Classifications of flowing sediment-water mixtures have, in the past, been based primarily on relative, qualitative differences in the style and rate of movement as well as on morphology and sedimentology of deposits. A more quantitative and physically relevant classification is presented here, based on thresholds in rhéologie behavior. The classif...

On 13 Nov. 1985 an eruption at Nevado del Ruiz rendered 30% of the 21 km2 ice-cap unstable. In spite of the small emission of tephra, the triggering of catastrophic lahars has been facilitated by the quick erosion and melting of 10% of the ice-cap volume and by the incorporation of thick fluvial and colluvial deposits from the valleys which have be...

Nearly instantaneous melting of snow and ice by the March 19, 1982, eruption of Mount St. Helens released a 4 × 106 m3 flood of water from the crater that was converted to a lahar (volcanic debris flow) through erosion and incorporation of sediment by the time it reached the base of the volcano. Over the next 81 km that it traveled down the Toutle...

Two large, high-velocity Iahars (volcanic debris flows) were triggered by a pyroclastic surge during the 1st few minutes of the May 18, 1980, eruption of Mount St. Helens. The initial surge cloud evolved progressively by gravity segregation from a gas-mobilized, highly inflated density flow to a dense, water-mobilized, basal debris flow (Iahar) and...

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lak...

Experimentation with a Hele-Shaw viscous-flow analogue apparatus has supported earlier suggestions, based on field evidence, that a causal link may exist between some soil pipes and slope failure. The analogue has shown that when a pipe is blocked, standing water will generate pore pressures in the surrounding soil matrix in proportion to the hydro...

The grass‐covered slopes on the southern flank of Mt Thomas, an upfaulted block of highly sheared sandstone and argillite 40 km NW of Christchurch, New Zealand, are presently undergoing severe erosion by a combination of mass‐wasting processes. Gully erosion, soil slips, and debris flows have carved out a number of steep, deeply incised ravines, fr...

Thesis (Ph. D.)--University of Washington, 1977. Includes bibliographical references (leaves [141]-149). Microfiche. s