Earth Sciences Commons^™

Focused Exhumation Along Megathrust Splay Faults In Prince William Sound, Alaska, Peter J. Haeussler, Phillip A. Armstrong, Lee M. Liberty, Kelly M. Ferguson, Shaun P. Finn, Jeanette C. Arkle, Thomas L. Pratt

Geosciences Faculty Publications and Presentations

Megathrust splay faults are a common feature of accretionary prisms and can be important for generating tsunamis during some subduction zone earthquakes. Here we provide new evidence from Alaska that megathrust splay faults have been conduits for focused exhumation in the last 5 Ma. In most of central Prince William Sound, published and new low-temperature thermochronology data indicate little to no permanent rock uplift over tens of thousands of earthquake cycles. However, in southern Prince William Sound on Montague Island, apatite (U–Th)/He ages are as young as 1.1 Ma indicating focused and rapid rock uplift. Montague Island lies in the …

Dynamical Precipitation Downscaling For Hydrologic Applications Using Wrf 4d-Var Data Assimilation: Implications For Gpm Era, Liao-Fan Lin, Ardeshir M. Ebtehaj, Rafael L. Bras, Alejandro N. Flores, Jingfeng Wang

Geosciences Faculty Publications and Presentations

The objective of this study is to develop a framework for dynamically downscaling spaceborne precipitation products using the Weather Research and Forecasting (WRF) Model with four-dimensional variational data assimilation (4D-Var). Numerical experiments have been conducted to 1) understand the sensitivity of precipitation downscaling through point-scale precipitation data assimilation and 2) investigate the impact of seasonality and associated changes in precipitation-generating mechanisms on the quality of spatiotemporal downscaling of precipitation. The point-scale experiment suggests that assimilating precipitation can significantly affect the precipitation analysis, forecast, and downscaling. Because of occasional overestimation or underestimation of small-scale summertime precipitation extremes, the numerical experiments presented …

Tectono-Metamorphic History Of The Eastern Taureau Shear Zone, Mauricie Area, Québec: Implications For The Exhumation Of The Mid-Crust In The Grenville Province, Renaud Soucy La Roche, Félix Gervais, Alain Tremblay, James L. Crowley, Gilles Ruffet

Geosciences Faculty Publications and Presentations

This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P–T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from …

Peat Formation Concentrates Arsenic Within Sediment Deposits Of The Mekong Delta, Jason W. Stuckey, Michael V. Schaefer, Benjamin D. Kocar, Jessica Dittmar, Juan Lezama Pacheco, Shawn G. Benner, Scott Fendorf

Geosciences Faculty Publications and Presentations

Mekong River Delta sediment bears arsenic that is released to groundwater under anaerobic conditions over the past several thousand years. The oxidation state, speciation, and distribution of arsenic and the associated iron bearing phases are crucial determinants of As reactivity in sediments. Peat from buried mangrove swamps in particular may be an important host, source, or sink of arsenic in the Mekong Delta. The total concentration, speciation, and reactivity of arsenic and iron were examined in sediments in a Mekong Delta wetland by X-ray fluorescence spectrometry (XRF), X-ray absorption spectroscopy (XAS), and selective chemical extractions. Total solid-phase arsenic concentrations in …

Exploring Radioisotopic Geochronology And Astrochronology, Stephen R. Meyers, Bradley S. Singer, Mark D. Schmitz

Geosciences Faculty Publications and Presentations

Numerical dating of the geologic record provides an essential framework for interpreting the rich history of our planet. Common applications include the determination of dates for extinction events and climate reorganizations, the assessment of rates of paleoenvironmental and paleobiologic change, and the correlation of rocks across vast expanses. Such investigations have yielded crucial insight into the mechanisms that shape Earth's surface environments over geologic time. But as geologists increasingly pursue high (spatial) resolution stratigraphic analyses in "deep time," the short temporal scales (<100,000 years) of the processes investigated push the limits of high-­precision geochronology.

Evidence For A Far-Traveled Thrust Sheet In The Greater Himalayan Thrust System, And An Alternative Model To Building The Himalaya, S. Khanal, D. M. Robinson, M. J. Kohn, S. Mandal

Geosciences Faculty Publications and Presentations

The Galchhi shear zone underlies the Kathmandu klippe in central Nepal and has emerged as a key structure for discriminating competing models for the formation of the Himalayan orogenic wedge. New chronologic data from the Galchhi area suggest a new structural and orogenic interpretation. Zircons from quartzites and an orthogneiss restrict protolith deposition to between 467+7/ – 10 Ma and ~570 Ma, with metamorphic zircon growth at 23-29 Ma. Comparable data from the Greater Himalayan Sequence (GHS) at the intra-GHS Langtang thrust, north of Galchhi, similarly restrict GHS deposition to between 475+7/ – 3 and ~660 Ma. Undeformed pegmatites near …

Early Permian Conodont Fauna And Stratigraphy Of The Garden Valley Formation, Eureka County, Nevada, Bruce R. Wardlaw, Dora M. Gallegos, Valery V. Chernykh, Walter S. Snyder

Geosciences Faculty Publications and Presentations

The lower part of the Garden Valley Formation yields two distinct conodont faunas. One of late Asselian age dominated by Mesogondolella and Streptognathodus and one of Artinskian age dominated by Sweetognathus with Mesogondolella. The Asselian fauna contains the same species as those found in the type area of the Asselian in the southern Urals including Mesogondolella dentiseparata, described for the first time outside of the Urals. Apparatuses for Sweetognathus whitei, Diplognathodus stevensi, and Idioprioniodus sp. are described. The Garden Valley Formation represents a marine pro-delta basin and platform, and marine and shore fan delta complex deposition. …

Magmatic Plumbing At Lucky Strike Volcano Based On Olivine-Hosted Melt Inclusion Compositions, V. D. Wanless, A. M. Shaw, M. D. Behn, S. A. Soule, J. Escartín, C. Hamelin

Geosciences Faculty Publications and Presentations

Here we present volatile, major, and trace element concentrations of 64 olivine-hosted melt inclusions from the Lucky Strike segment on the mid-Atlantic ridge. Lucky Strike is one of two locations where a crustal melt lens has been seismically imaged on a slow-spreading ridge. Vapor-saturation pressures, calculated from CO₂ and H₂O contents of Lucky Strike melt inclusions, range from approximately 300-3000 bars, corresponding to depths of 0.5-9.9 km below the seafloor. Approximately 50% of the melt inclusions record crystallization depths of 3-4 km, corresponding to the seismically imaged melt lens depth, while an additional ∼35% crystallize at depths …

Thermal Damping And Retardation In Karst Conduits, A. J. Luhmann, Matthew D. Covington, J. M. Myre, Matija Perne, S. W. Jones, E. C. Alexander Jr., M. O. Saar

Geosciences Faculty Publications and Presentations

Water temperature is a non-conservative tracer in the environment. Variations in recharge temperature are damped and retarded as water moves through an aquifer due to heat exchange between water and rock. However, within karst aquifers, seasonal and short-term fluctuations in recharge temperature are often transmitted over long distances before they are fully damped. Using analytical solutions and numerical simulations, we develop relationships that describe the effect of flow path properties, flow-through time, recharge characteristics, and water and rock physical properties on the damping and retardation of thermal peaks/troughs in karst conduits. Using these relationships, one can estimate the thermal retardation …

Consider A Cylindrical Cave: A Physicist's View Of Cave And Karst Science, Matthew D. Covington, Matija Perne

Geosciences Faculty Publications and Presentations

We review the current understanding of the physics of caves and karst. Our review focuses on research that has used simple physically based models to improve understanding of processes that occur in karst. The topics we cover include cave atmosphere dynamics, transport within karst conduits, and models of speleogenesis and related processes. We highlight recent advances in these subjects and attempt to identify promising areas for future work. In our judgment, many of the most intriguing open questions relate to the interactions between these three groups of processes.

Mapping Thunder Sources By Inverting Acoustic And Electromagnetic Observations, J. F. Anderson, J. B. Johnson, R. O. Arechiga, R. J. Thomas

Geosciences Faculty Publications and Presentations

We present a new method of locating current flow in lightning strikes by inversion of thunder recordings constrained by Lightning Mapping Array observations. First, radio frequency (RF) pulses are connected to reconstruct conductive channels created by leaders. Then, acoustic signals that would be produced by current flow through each channel are forward modeled. The recorded thunder is considered to consist of a weighted superposition of these acoustic signals. We calculate the posterior distribution of acoustic source energy for each channel with a Markov Chain Monte Carlo inversion that fits power envelopes of modeled and recorded thunder; these results show which …

Urban Seismology For Groundwater Characterization In A Developing Country: Challenges And Rewards, John H. Bradford, Kyle Lindsay, Steve Silliman, Nicaise Yalo, Moussa Boukari

Geosciences Faculty Publications and Presentations

The coastal city of Cotonou in the developing country of Bénin, West Africa, is a large population center that is facing a serious threat to the sustainability of its freshwater supply. The city relies on the Godomey aquifer for domestic water, but the aquifer is undergoing saltwater intrusion. This problem is likely to worsen without significant steps to improve management of the water supply. Aquifer continuity and saltwater flow paths are poorly understood, but that information is critical to ensure sustainable access to freshwater in this growing urban center. In January 2012, a two-year geophysical investigation was begun with the …

Quantifying The Basal Conditions Of A Mountain Glacier Using A Targeted Full-Waveform Inversion: Bench Glacier, Alaska, Usa, E. Babcock, J. Bradford

Geosciences Faculty Publications and Presentations

Glacier dynamics are inextricably linked to the basal conditions of glaciers. Seismic reflection methods can image the glacier bed under certain conditions. However, where a seismically thin layer of material is present at the bed, traditional analyses may fail to fully characterize bed properties. We use a targeted full-waveform inversion algorithm to quantify the basal-layer parameters of a mountain glacier: thickness (d), P-wave velocity (α) and density (ρ). We simultaneously invert for the seismic quality factor (Q) of the bulk glacier ice. The inversion seeks to minimize the difference between the data …

Turbidity-Based Sediment Monitoring In Northern Thailand: Hysteresis, Variability, And Uncertainty, Shawn G. Benner, Spencer H. Wood

Geosciences Faculty Publications and Presentations

Annual total suspended solid (TSS) loads in the Mae Sa River in northern Thailand, determined with an automated, turbidity-based monitoring approach, were approximately 62,000, 33,000, and 14,000 Mg during the three years of observation. These loads were equivalent to basin yields of 839 (603-1170), 445 (217-462), and 192 (108-222) Mg km^-2 for the 74.16-km² catchment during 2006, 2007, and 2008, respectively. The yearly uncertainty ranges indicate our loads may be underestimated by 38-43% or overestimated by 28-33%. In determining the annual loads, discharge (Q) and turbidity (T) values were compared against 333 hand-sampled total suspended solid concentrations (TSS) …

Warm Water Benthic Foraminifera Document The Pennsylvanian-Permian Warming And Cooling Events – The Record From The Western Pangea Tropical Shelves, Vladimir Davydov

Geosciences Faculty Publications and Presentations

Shallow warm water benthic foraminifera (SWWBF), including all larger fusulinids (symbiont-bearing benthic foraminifera), are among the best indicators of paleoclimate and paleogeography in the Carboniferous and Permian. The distribution of benthic foraminifera in space and time constrain important tectonic, paleogeographic and climatic events at a global scale. The North American shelves during Pennsylvanian and Permian time - though geographically within the tropical belt - are characterized by temperate environments with significantly lower foraminifera diversification and rare occurrences of warm water Tethyan forms, that are in general appear in the region as a migration entities. Such environments allow documentation of warming …

Comparing Near-Regional And Local Measurements Of Infrasound From Mount Erebus, Antarctica: Implications For Monitoring, A. L. Dabrowa, D. N. Green, J. B. Johnson, J. C. Phillips, A. C. Rust

Geosciences Faculty Publications and Presentations

Local (100s of meters from vent) monitoring of volcanic infrasound is a common tool at volcanoes characterized by frequent low-magnitude eruptions, but it is generally not safe or practical to have sensors so close to the vent during more intense eruptions. To investigate the potential and limitations of monitoring at near-regional ranges (10s of km) we studied infrasound detection and propagation at Mount Erebus, Antarctica. This site has both a good local monitoring network and an additional International Monitoring System infrasound array, IS55, located 25 km away. We compared data recorded at IS55 with a set of 117 known Strombolian …

Application Of The Monopole Source To Quantify Explosive Flux During Vulcanian Explosions At Sakurajima Volcano (Japan), Jeffrey B. Johnson, Alex J. C. Miller

Geosciences Faculty Publications and Presentations

A primary goal in volcano seismology is to characterize source motions internal to a volcano in terms of their representative forces. In a similar manner, much volcano infrasound research strives to recover eruptive force time histories corresponding to material accelerations occurring at Earth’s free surface. These motions may correspond to explosive emission of gas and pyroclasts (e.g., Banister, 1984), rapid ground distensions of a volcanic dome (e.g., Johnson and Lees, 2010), and/or gravity driven rock fall or pyroclastic flows (e.g., Yamasato, 1997). When free surface motion is unsteady it imposes stresses upon the surrounding atmosphere, which are propagated as acoustic …

Introduction To An Open Community Infrasound Dataset From The Actively Erupting Sakurajima Volcano, Japan, David Fee, Akihiko Yokoo, Jeffrey B. Johnson

Geosciences Faculty Publications and Presentations

Active volcanoes are significant sources of seismic and acoustic radiation. Extensive work has shown that infrasound is an effective tool to study and monitor active volcanoes. Infrasound is now a regular tool utilized by volcano observatories to aid in volcano monitoring and hazard mitigation. Infrasound‐based studies are able to provide important information on eruption dynamics and to develop quantitative models of volcanic eruptions. In addition, volcanoes provide excellent acoustic sources for atmospheric propagation studies and can be used to infer atmospheric dynamics and structure (see Johnson and Ripepe, 2011; Fee and Matoza, 2013 for recent reviews on volcano infrasound). The …

Eocene-Oligocene Latitudinal Climate Gradients In North America Inferred From Stable Isotope Ratios In Perissodactyl Tooth Enamel, Alessandro Zanazzi, Emily Judd, Andrew Fletcher, Harold Bryant, Matthew J. Kohn

Geosciences Faculty Publications and Presentations

The Eocene-Oligocene transition (~ 34 Ma) was one of the most pronounced episodes of climate change of the Cenozoic. In order to investigate this episode of global climate cooling in North America, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl (horse and rhino) tooth enamel samples from the Eocene-Oligocene rocks of the Cypress Hills Formation (southwestern Saskatchewan, Canada); we then compared the results with previously published data from the US Great Plains (Nebraska, South Dakota, and Wyoming).

Average (± 1σ) perissodactyl enamel δ¹³C values (vs. V-PDB) in the Eocene (-8.8 …

Explosive Dome Eruptions Modulated By Periodic Gas-Driven Inflation, Jeffrey B. Johnson, J. J. Lyons, B. J. Andrews, J. M. Lees

Geosciences Faculty Publications and Presentations

Volcan Santiaguito (Guatemala) “breathes” with extraordinary regularity as the edifice's conduit system accumulates free gas, which periodically vents to the atmosphere. Periodic pressurization controls explosion timing, which nearly always occurs at peak inflation, as detected with tiltmeters. Tilt cycles in January 2012 reveal regular 26 ± 6 min inflation/deflation cycles corresponding to at least ~10¹ kg/s of gas fluxing the system. Very long period (VLP) earthquakes presage explosions and occur during cycles when inflation rates are most rapid. VLPs locate ~300 m below the vent and indicate mobilization of volatiles, which ascend at ~50 m/s. Rapid gas ascent feeds …

Luminescence Dating Without Sand Lenses: An Application Of Osl To Coarse-Grained Alluvial Fan Deposits Of The Lost River Range, Idaho, Usa, M. K. Kenworthy, T. M. Rittenour, J. L. Pierce, N. A. Sutfin, W. D. Sharp

Geosciences Faculty Publications and Presentations

Optically stimulated luminescence (OSL) dating is increasingly used to estimate the age of fluvial deposits. A significant limitation, however, has been that conventional techniques of sampling and dose rate estimation are suitable only for thick (>60 cm) layers consisting of sand size or finer grains. Application of OSL dating to deposits lacking such layers remains a significant challenge. Alluvial fans along the western front of the Lost River Range in east-central Idaho, USA are one example. Deposits are typically pebble to cobble sheetflood gravels with a sandy matrix but thin to absent sand lenses. As a result, the majority …

The Spatial Cross-Correlation Method For Dispersive Surface Waves, Andrew P. Lamb, Kasper Van Wijk, Lee M. Liberty, T. Dylan Mikesell

Geosciences Faculty Publications and Presentations

Dispersive surface waves are routinely used to estimate the subsurface shear-wave velocity distribution, at all length scales. In the well-known Spatial Autocorrelation method, dispersion information is gained from the correlation of seismic noise signals recorded on the vertical (or radial) components. We demonstrate practical advantages of including the cross-correlation between radial and vertical components of the wavefield in a spatial cross-correlation method. The addition of cross-correlation information increases the resolution and robustness of the phase velocity dispersion information, as demonstrated in numerical simulations and a near-surface field study with active seismic sources, where our method confirms the presence of a …

Calculating The Velocity Of A Fast-Moving Snow Avalanche Using An Infrasound Array, Scott Havens, Hans-Peter Marshall, Jeffrey B. Johnson, Bill Nicholson

Geosciences Faculty Publications and Presentations

On 19 January 2012, a large D3 avalanche (approximately 10³ t) was recorded with an infrasound array ideally situated for observing the avalanche velocity. The avalanche crossed Highway 21 in Central Idaho during the largest avalanche cycle in the 15 years of recorded history and deposited approximately 8 m of snow on the roadway. Possible source locations along the avalanche path were estimated at 0.5 s intervals and were used to calculate the avalanche velocity during the 64 s event. Approximately 10 s prior to the main avalanche signal, a small infrasound signal originated from the direction of the …

Postglacial Early Permian (Late Sakmarian– Early Artinskian) Shallow-Marine Carbonate Deposition Along A 2000 Km Transect From Timor To West Australia, Vladimir I. Davydov

Geosciences Faculty Publications and Presentations

Late Sakmarian to early Artinskian (Early Permian) carbonate deposition was widespread in the marine intracratonic rift basins that extended into the interior of Eastern Gondwana from Timor in the north to the northern Perth Basin in the south. These basins spanned about 20° of paleolatitude (approximately 35°S to 55°S). This study describes the type section of the Maubisse Limestone in Timor-Leste, and compares this unit with carbonate sections in the Canning Basin (Nura Nura Member of the Poole Sandstone), the Southern Carnarvon Basin (Callytharra Formation) and the northern Perth Basin (Fossil Cliff Member of the Holmwood Shale). The carbonate units …

Discovery Of Shallow-Marine Biofacies Conodonts In A Bioherm Within The Carboniferous-Permian Transition In The Omalon Massif, Ne Russia Near The North Paleo-Pole: Correlation With A Warming Spike In The Southern Hemisphere, Vladimir I. Davydov, Alexander S. Biakov

Geosciences Faculty Publications and Presentations

The conodont genera Hindeodus and Streptognathodus are reported for the first time within the Carboniferous-Permian transition in the northern high latitudes of the Paren’ River, Omolon Massif, NE Russia. Several fossil groups, including brachiopods, bivalves, scaphopods and microgastropods were found to be prolific in the invertebrate-dominated bioherms. These bioherms occur within predominantly siliciclastic sequences with extremely poor fauna, whereas in the studied bioherms the diversity of the bivalves and brachiopods exceeded observed diversity elsewhere in coeval facies in NE Russia. The bioherms are biostratigraphically constrained as uppermost Pennsylvanian to lowermost Cisuralian based on ammonoids. The very unusual peak of bivalve …

Independent Evaluation Of The Snodas Snow Depth Product Using Regional Scale Lidar-Derived Measurements, A. R. Hedrick, H. P. Marshall, A. Winstral, K. Elder, S. Yueh, D. Cline

Geosciences Faculty Publications and Presentations

Repeated Light Detection and Ranging (LiDAR) surveys are quickly becoming the de facto method for measuring spatial variability of montane snowpacks at high resolution. This study examines the potential of a 750 km² LiDAR-derived dataset of snow depths, collected during the 2007 northern Colorado Cold Lands Processes Experiment (CLPX-2), as a validation source for an operational hydrologic snow model. The SNOw Data Assimilation System (SNODAS) model framework, operated by the US National Weather Service, combines a physically-based energy-and-mass-balance snow model with satellite, airborne and automated ground-based observations to provide daily estimates of snowpack properties at nominally 1 km resolution …

U-Pb Zircon Geochronology Of Roxbury Conglomerate, Boston Basin, Massachusetts: Tectono-Stratigraphic Implications For Avalonia In And Beyond Se New England, Margaret D. Thompson, Jahandar Ramezani, James L. Crowley

Geosciences Faculty Publications and Presentations

High-precision CA-TIMS ²⁰⁶Pb/²³⁸U zircon dates from sandstone and Brighton igneous rocks associated with Roxbury Conglomerate in the Boston Basin, eastern Massachusetts provide constraints on the age and tectonic significance of these deposits. Detrital zircon suites from Roxbury-related sandstones representing, in ascending order, the Franklin Park Member (proposed name), the Brookline Member and the Squantum Member establish closely comparable maximum depositional ages of 595.14 ± 0.90, 598.87 ± 0.71 and 596.39 ± 0.79 Ma, respectively. The youngest of these is the best maximum age estimate of the conglomerate. Brighton dacite near the base of the Brookline Member and …

Soil, Snow, Weather, And Sub-Surface Storage Data From A Mountain Catchment In The Rain–Snow Transition Zone, P. R. Kormos, D. Marks, C. J. Williams, H. P. Marshall, Pam Aishlin, D. G. Chandler, James P. Mcnamara

Geosciences Faculty Publications and Presentations

A comprehensive hydroclimatic data set is presented for the 2011 water year to improve understanding of hydrologic processes in the rain-snow transition zone. This type of dataset is extremely rare in scientific literature because of the quality and quantity of soil depth, soil texture, soil moisture, and soil temperature data. Standard meteorological and snow cover data for the entire 2011 water year are included, which include several rain-on-snow events. Surface soil textures and soil depths from 57 points are presented as well as soil texture profiles from 14 points. Meteorological data include continuous hourly shielded, unshielded, and wind corrected precipitation, …

A Combined Field And Numerical Approach To Understanding Dilute Pyroclastic Density Current Dynamics And Hazard Potential: Auckland Volcanic Field, New Zealand, Brittany D. Brand, Darren Gravley, Amanda Clarke, Jan Lindsay, Simon H. Boomberg, Javier Agustin-Flores, Károly Németh

Geosciences Faculty Publications and Presentations

The most dangerous and deadly hazards associated with phreatomagmatic eruption in the Auckland Volcanic Field (AVF; Auckland, New Zealand) are those related to volcanic base surges - dilute, ground-hugging, particle laden currents with dynamic pressures capable of severe to complete structural damage. We use the well-exposed base surge deposits of the Maungataketake tuff ring, (Manukau coast, Auckland) to reconstruct flow dynamics and destructive potential of base surges produced during the eruption. The initial base surge(s) snapped trees up to 0.5 m in diameter near their base as far as 0.7-0.9 km from the vent. Beyond this distance the trees were …

Dynamics Of Pyroclastic Density Currents: Conditions That Promote Substrate Erosion And Self-Channelization - Mount St Helens, Washington (Usa), Brittany D. Brand, Chelsea Mackaman-Lofland, Nicholas M. Pollock, Sylvana Bendaña, Blaine Dawson, Pamela Wichgers

Geosciences Faculty Publications and Presentations

The May 18th, 1980 eruption of Mount St. Helens (MSH) produced multiple pyroclastic density currents (PDCs), burying the area north of the volcano under 10s of meters of deposits. Detailed measurements of recently exposed strata from these PDCs provide substantial insight into the dynamics of concentrated currents including inferences on particle-particle interactions, current mobility due to sedimentation fluidization and internal pore pressure, particle support mechanisms, the influence of surface roughness and the conditions that promote substrate erosion and self-channelization. Four primary flow units are identified along the extensive drainage system north of the volcano. Each flow unit has intricate vertical …