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1. Tracking secondary lahar flow paths and characterizing pulses and surges using infrasound array networks at Volcán de Fuego, Guatemala

   https://doi.org/10.30909/vol.04.02.239256  

   Bosa, Ashley; Johnson, Jeffrey; De Angelis, Silvio; Lyons, John; Roca, Amilcar; Anderson, Jacob; Pineda, Armando (October 2021, Volcanica)

   Lahars are one of the greatest hazards at many volcanoes, including Volcán de Fuego (Guatemala). On 1 December 2018 at 8:00pm local Guatemala time (2:00:00 UTC), an hour-long lahar event was detected at Volcán de Fuego by two permanent seismo-acoustic stations along the Las Lajas channel on the southeast side. To establish the timing, duration, and speed of the lahar, infrasound array records were examined to identify both the source direction(s) and the correlated energy fluctuations at the two stations. Co-located seismic and acoustic signals were also examined, which indicated at least 5 distinct energy pulses within the lahar record.  We infer that varying sediment load and/or changes in flow velocity is shown by clear fluctuations in the acoustic and seismic power recorded at one of the stations. This particular event studied with infrasound provides insight into how lahars occur around Volcán de Fuego. 

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2. Formation, Development, and Propagation of a Rare Coastal Coccolithophore Bloom

   https://doi.org/10.1029/2019JC015072  

   Matson, Paul G.; Washburn, Libe; Fields, Erik A.; Gotschalk, Chris; Ladd, Tanika M.; Siegel, David A.; Welch, Zoë S.; Iglesias‐Rodriguez, M. Debora (May 2019, Journal of Geophysical Research: Oceans)

   Abstract This study examines an unprecedented bloom ofEmiliania huxleyialong the California coast during the NE Pacific warm anomaly of 2014–2015. Observations of coccolithophore populations from microscopy and flow cytometry, surface current data derived from high‐frequency radar, and satellite ocean color imagery were used to track the population dynamics of the bloom in the Santa Barbara Channel. Results show a coastal bloom of mostlyE. huxleyithat reached cell concentrations up to 5.7 × 10⁶cells per liter and a maximum spatial extent of 1,220 km². We speculate that the rare cooccurrence of warm water, high water column stability, and an extensive preceding diatom bloom during the anomaly contributed to the development of this bloom. Flow cytometry measurements provided insight on the phases of bloom development (e.g., growth versus senescence) with calcified cells comprising up to 64% of particles containing chlorophyll a and detached‐coccolith:cell ratios ranging from 10 to >100. Lagrangian particle trajectories estimated during two nonoverlapping 48‐ and 72‐hr periods showed the changes in the surface structure of the bloom due to advection by surface currents and nonconservative biological and physical processes. Time rates of change of particulate inorganic carbon were estimated along particle trajectories, with rates ranging from −4 to 6 μmol·L⁻¹·day⁻¹. The approach presented here is likely to be useful for understanding the evolution of coastal phytoplankton bloom events in a general setting. 

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3. Revitalized Karuk and Yurok cultural burning to enhance California hazelnut for basketweaving in northwestern California, USA

   https://doi.org/10.1186/s42408-021-00092-6  

   Marks-Block, Tony; Lake, Frank K.; Bliege Bird, Rebecca; Curran, Lisa M. (December 2021, Fire Ecology)

   null (Ed.)

   Resumen Antecedentes Las tribus Karuk y Yurok del noroeste de California, EEUU, están revitalizando la práctica cultural de quemas, que es el uso del fuego prescripto para aumentar las especies culturalmente importantes. Estas quemas culturales son críticas para sustentar la vida de los pueblos indígenas, y fueron sumamente extendidas antes del establecimiento de las políticas de exclusión del fuego. Uno de los principales objetivos de las quemas culturales es aumentar la producción de tallos del avellano de California ( Corylus cornuta Marsh var. californica ) que es usado para la construcción de cestos por los fabricantes de cestos (cesteros) de las tribus Karuk y Yurok. Para evaluar las quemas culturales como una forma de ingeniería ecosistémica, monitoreamos la producción de cestos realizados con tallos de avellano, la calidad y densidad de esos tallos, en 48 parcelas (400 m 2 ) dentro de dos quemas prescriptas y en 19 lugares con quemas culturales. Las variables socio-ecológicas que fueron analizadas incluyeron la frecuencia de quemas, la estación de quemas, el área basal (≥10 cm de diámetro a la altura del pecho) de árboles del dosel superior, el ramoneo por ungulados, y la exposición. Observamos asimismo el lugar de colección de los tallos para comparar distancias recorridas, tasas de recolección, y las preferencias de quienes fabrican los cestos a través de sitios con diferentes historias de fuego y tenencia de la tierra. Resultados Una estación luego del fuego, los arbustos de avellano de California produjeron un incremento de 13 veces la producción de tallos factibles de ser usados en cestería comparados con arbustos creciendo al menos tres estaciones post fuego ( P < 0.0001). La producción y el largo de los tallos desarrollaron relaciones negativas con el área basal de árboles del dosel superior ( P < 0.01) y el ramoneo de ungulados ( P < 0.0001). Las parcelas quemadas a alta frecuencia (al menos tres eventos de fuego de 1989 a 2019) tuvieron 1,86 veces más arbustos de avellano que aquellas parcelas que experimentaron menos de tres eventos de fuego ( P < 0.0001), y fueron todos ubicados en la reservación de Yurok, donde la tenencia de la tierra por parte de la comunidad indígena es comparativamente más fuerte. Los fabricantes de cestos viajaron distancias 3,8 veces más largas para alcanzar lugares quemados por fuegos naturales comparados con aquellos que fueron sujetos a quemas cultuales prescriptas ( P < 0.01). En los sitios quemados por prácticas culturales, por incendios naturales u aquellos lugares excluidos de fuegos, el tiempo promedio de recolección fue de 4,9, 1,6, y 0.5 tallos por minuto por individuo, respectivamente. Conclusiones Los regímenes de quemas culturales por parte de las tribus Karuk y Yurok con altas frecuencias de quema ( e,g, de tres a cinco años), promueven una alta densidad de arbustos de avellano e incrementan la producción de tallos para cestería. Esto mejora la eficiencia en la recolección y reduce los costos del viaje, lo que ayuda a la revitalización de una práctica cultural vital. Nuestros hallazgos proveen evidencias positivas de ingeniería ecosistémica humana, y muestran que el incremento de la soberanía tribal sobre el manejo de fuego mejora las condiciones de bienestar socio-económico, mientras que al mismo tiempo aportan a la estructura y el funcionamiento del ecosistema. 

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4. Intermittent Channel Systems of a Low‐Relief, Low‐Gradient Floodplain: Comparison of Automatic Extraction Methods

   https://doi.org/10.1029/2020WR027603  

   Xu, H.; van der Steeg, S.; Sullivan, J.; Shellye, D.; Cely, J. E.; Viparelli, E.; Lakshmi, V.; Torres, R. (September 2020, Water resources research)

   null (Ed.)

   Intermittent floodplain channels are low‐relief conduits etched into the floodplain surface and remain dry much of the year. These channels comprise expansive systems and are important because during low‐level inundation they facilitate lateral hydraulic connectivity throughout the floodplain. Nevertheless, few studies have focused on these floodplain channels due to uncertainty in how to identify and characterize these systems in digital elevation models (DEMs). In particular, their automatic extraction from widely available DEMs is challenging due to the characteristically low‐relief and low‐gradient topography of floodplains. We applied three channel extraction approaches to the Congaree River floodplain DEM and compared the results to a channel reference map created through numerous field excursions over the past 30 years. The methods that we tested are based on flow accumulation area, topographic curvature, and mathematical morphology, or the D8, Laplacian, and bottom‐hat transform (BHT), respectively. Of the 198 km of reference channels the BHT, Laplacian, and D8 extracted 83%, 71%, and 23%, respectively, and the BHT consistently had the highest agreement with the reference network at the local (5 m) and regional (10 km) scales. The extraction results also include commission “error”, augmenting the reference map with about 100 km of channel length. Overall, the BHT method provided the best results for channel extraction, giving over 298 km in 69 km2 with a detrended regional relief of 1.9 m. Further, these analyses allow us to shed light on the meaning and use of the term “low‐relief landscapes”. 

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5. Rates of bedrock canyon incision by megafloods, Channeled Scabland, eastern Washington, USA

   https://doi.org/10.1130/B36975.1  

   Lehnigk, Karin E; Larsen, Isaac J; Lamb, Michael P; David, Scott R (April 2024, Geological Society of America Bulletin)

   Abstract Pleistocene outburst floods from the drainage of glacial Lake Missoula carved bedrock canyons into the Columbia Plateau in eastern Washington, USA, forming the Channeled Scabland. However, rates of bedrock incision by outburst floods are largely unconstrained, which hinders the ability to link flood hydrology with landscape evolution in the Channeled Scabland and other flood-carved landscapes. We used long profiles of hanging tributaries to reconstruct the pre-flood topography of the two largest Channeled Scabland canyons, upper Grand Coulee and Moses Coulee, and a smaller flood-eroded channel, Wilson Creek. The topographic reconstruction indicates floods eroded 67.8 km3, 14.5 km3, and 1.6 km3 of rock from upper Grand Coulee, Moses Coulee, and Wilson Creek, respectively, which corresponds to an average incision depth of 169 m, 56 m, and 10 m in each flood route. We simulated flood discharge over the reconstructed, pre-flood topography and found that high-water evidence was emplaced in each of these channels by flow discharges of 3.1 × 106 m3 s−1, 0.65–0.9 × 106 m3 s−1, and 0.65–0.9 × 106 m3 s−1, respectively. These discharges are a fraction of those predicted under the assumption that post-flood topography was filled to high-water marks for Grand and Moses Coulees. However, both methods yield similar results for Wilson Creek, where there was less erosion. Sediment transport rates based on these discharges imply that the largest canyons could have formed in only about six or fewer floods, based on the time required to transport the eroded rock from each canyon, with associated rates of knickpoint propagation on the order of several km per day. Overall, our results indicate that a small number of outburst floods, with discharges much lower than commonly assumed, can cause extensive erosion and canyon formation in fractured bedrock. 

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