SEARCH · Geology Reports

Results for “Journal of Morphology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources

USGS1997

Winter activity patterns of American martens ( Martes americana ): Rejection of the hypothesis of thermal-cost minimization

Despite their temperate to subarctic geographic range, American martens ( Martes americana ) possess a thermally inefficient morphology. The lack of morphological adaptations for reducing thermal costs suggests that marten may use behavioral strategies to optimize thermal budgets. During the winters of 1989–1990 and 1990–1991, we radio-collared and monitored the diel activity of 7 martens. A log-linear model suggested that the presence or absence of light was the only factor associated with marten activity patterns ( p < 0.001). A regression of the percentage of active fixes on ambient temperature failed to detect an association ( b = −4.45, p = 0.084, n = 12). Contents of marten scats suggested that their activity was consistent with the prey-vulnerability hypothesis. While martens must balance multiple life requisites, their activity patterns suggest that they accept increased thermal costs in order to increase foraging efficiency. However, the nocturnal activity of martens during winter was also consistent with the hypothesis that they may be able to limit their own exposure to predation risk. The nocturnal habits of Newfoundland martens in the winter were consistent with the hypothesis of avoidance of predation risk.

Newfoundland↗

USGS2012

Probabilistic prediction of barrier-island response to hurricanes

Prediction of barrier-island response to hurricane attack is important for assessing the vulnerability of communities, infrastructure, habitat, and recreational assets to the impacts of storm surge, waves, and erosion. We have demonstrated that a conceptual model intended to make qualitative predictions of the type of beach response to storms (e.g., beach erosion, dune erosion, dune overwash, inundation) can be reformulated in a Bayesian network to make quantitative predictions of the morphologic response. In an application of this approach at Santa Rosa Island, FL, predicted dune-crest elevation changes in response to Hurricane Ivan explained about 20% to 30% of the observed variance. An extended Bayesian network based on the original conceptual model, which included dune elevations, storm surge, and swash, but with the addition of beach and dune widths as input variables, showed improved skill compared to the original model, explaining 70% of dune elevation change variance and about 60% of dune and shoreline position change variance. This probabilistic approach accurately represented prediction uncertainty (measured with the log likelihood ratio), and it outperformed the baseline prediction (i.e., the prior distribution based on the observations). Finally, sensitivity studies demonstrated that degrading the resolution of the Bayesian network or removing data from the calibration process reduced the skill of the predictions by 30% to 40%. The reduction in skill did not change conclusions regarding the relative importance of the input variables, and the extended model's skill always outperformed the original model.

Florida↗

USGS2018

Ecohydrologic changes caused by hydrologic disconnection of ephemeral stream channels in Mojave National Preserve, California

Emplacement of highways and railroads has altered natural hydrologic systems by influencing surface-water flow paths and biotic communities in Mojave National Preserve. Infiltration experiments were conducted along active and abandoned channels to evaluate changes in hydrology and related effects on plant water availability and use. Simulated rainfall infiltration experiments with vegetation monitoring were conducted along an active channel upslope and a comparable abandoned channel down slope of the transportation corridor. We also conducted 90 single-ring, ponded infiltration experiments in adjacent channels to evaluate field-saturated hydraulic conductivity and particle size distributions. The abandoned channels are still morphologically evident, but are disconnected from runoff sources at higher elevations. Infiltration test results show that water infiltrates twice as fast in the active channels. Excavation showed weak soil development with fewer plant roots beneath the abandoned channel. SEM analysis on surface samples showed the presence of cyanobacteria only in abandoned channels. Plants up to three meters away from both channels showed physiological responses to channel water applied in a simulated pulse of rain. The response was short-lived and less pronounced for plants adjacent to the abandoned channel, whereas those adjacent to the active channel showed responses up to two months after the pulse. These responses may explain observed lower plant densities and fewer deep-rooted species along abandoned channels compared to active channels. We infer that the deeper-rooting plants are more abundant where they are able to take advantage of the increased soil-water storage resulting from greater infiltration and flow frequency in active stream channels.

California↗

USGS2004

Granular avalanches across irregular three-dimensional terrain: 2. Experimental tests

Scaling considerations indicate that miniature experiments can be used to test models of granular avalanches in which the effects of intergranular fluid and cohesion are negligible. To test predictions of a granular avalanche model described in a companion paper, we performed bench top experiments involving avalanches of dry sand across irregular basal topography that mimicked the complexity of natural terrain. The experiments employed a novel method of laser-assisted cartography to map the three-dimensional morphology of rapidly moving avalanches, thereby providing high-resolution data for comparison with model output. Model input consisted of two material properties (angles of internal and basal Coulomb friction of the sand), which were measured in independent tests, and of initial and boundary conditions that characterized the geometry of the experimental apparatus. Experimental results demonstrate that the model accurately predicts not only the gross behavior but also many details of avalanche motion, from initiation to deposition. We attribute this accuracy to a mathematical and computational formulation that conserves mass and momentum in three-dimensional physical space and satisfies the Coulomb equation in three-dimensional stress space. Our results support the hypothesis that a Coulomb proportionality between shear and normal stresses applies in moderately rapid granular flows and that complicated constitutive postulates are unnecessary if momentum conservation is strictly enforced in continuum avalanche models. Furthermore, predictions of our Coulomb continuum model contrast with those of a Coulomb point mass model, illustrating the importance of multidimensional modeling and model testing.

Journal of Geophysical Research Earth Surface↗

USGS2007

Sorted bed forms as self-organized patterns: 2. complex forcing scenarios

We employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions. Results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated, a priori unpredictable, behavior. This happens because the system responds to a change in wave characteristics by attempting to self-organize into a patterned seabed of different geometry and spacing. The new wavelength might not have enough time to emerge before a new change in wave characteristics occurs, leading to less regular seabed configurations. The new seabed configuration is also highly dependent on the preexisting morphology, which further limits the possibility of predicting future behavior. For the same reasons, variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms. Spatial variability in grain size distribution and different types of net sediment aggradation/degradation can also result in the development of sorted bed forms characterized by a less regular shape. Numerical simulations qualitatively agree with observed geometry (spacing and height) of sorted bed forms. Also in agreement with observations is that at shallower depths, sorted bed forms are more likely to be affected by changes in the forcing conditions, which might also explain why, in shallow waters, sorted bed forms are described as ephemeral features. Finally, simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms. Instead, variations in sorted bed form characteristics may result from variations in local hydrodynamic and/or sedimentary conditions.

Journal of Geophysical Research F: Earth Surface↗

USGS2020

Fluorescence spectroscopy of ancient sedimentary organic matter via confocal laser scanning microscopy (CLSM)

Fluorescence spectroscopy via confocal laser scanning microscopy (CLSM) was used to analyze ancient sedimentary organic matter, including Tasmanites microfossils in Devonian shale and Gloecapsomorpha prisca ( G. prisca ) in Ordovician kukersite from North American basins. We examined fluorescence emission as a function of excitation laser wavelength, sample orientation, and with respect to location within individual organic entities and in transects across bedded organic matter. Results from spectral scans of the same field of view in Tasmanites with different laser lines showed progressive red-shift in emission maxima with longer excitation wavelengths. This result indicates steady-state Tasmanites fluorescence emission is an overlapping combination of emission from multiple fluorophore functions. Stokes shift decreased with increasing excitation wavelength, further suggesting the presence of multiple fluorophore functions with different S 1 → S 0 transition energies. This observation also indicates that at longer excitation wavelengths, less absorbed light energy is dissipated via collisional transfer than at shorter excitation wavelengths and may suggest fewer polar functions are preferentially absorbing. Confirming earlier results, emission spectra observed from high fluorescence intensity regions (fold apices) in individual Tasmanites are blue-shifted relative to emission from other locations in the same microfossil. We suggest high intensity emission is from photoselective alignment of polarized excitation with the fluorophore absorption and emission transition moment. The blue shift observed in regions of high intensity emission may be due to relative absence or realignment of polar species, e.g., bridging ether or ester functions, although variations in O abundance could not be confirmed with preliminary time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis. Tasmanites occurring in consolidated sediments are flattened from original spherical morphology and, in optical microscopy, this burial deformation results in generally parallel extinction (strain-influenced) and positive elongation. The deformation also induces fluorescence anisotropy observed as variations in emission wavelength when individual Tasmanites are measured from their long axis parallel to bedding, whereas this effect is absent in bedding-normal view. Transects from G. prisca -rich source layers into adjacent reservoir layers show decrease in fluorescence intensity and spectral red-shift (increase in full-width half-maximum with increasing red portion of the half-width). These results may suggest an increase in fluorescence quenching across the source-to-reservoir transition zone, consistent with an increase in aromaticity following petroleum expulsion and migration. These observations are supported by increasing reflectance values measured across similar micro-scale transects. Our results highlight the applicability of CLSM as a broad and under-utilized approach for the characterization of sedimentary organic matter and are discussed with perspective toward petroleum processes and thermal indices research.

International Journal of Coal Geology↗

USGS2022

Evidence for fluctuating wind in shaping an ancient Martian dune field: The Stimson formation at the Greenheugh pediment, Gale crater

Temporal fluctuations of wind strength and direction can influence aeolian bedform morphology and orientation, which can be encoded into the architecture of aeolian deposits. These strata represent a direct record of atmospheric processes and can be used to understand ancient Martian atmospheric processes as well as those on Earth. The strata can: give insight to ancient atmospheric circulation, how the atmosphere evolved in response to global changes in habitability, and how ancient processes differ from modern processes. The Stimson formation at the Greenheugh pediment (Gale crater) records evidence of fluctuating wind across multiple temporal scales. The strata can be subdivided into three intervals–Gleann Beag, Ladder, and Edinburgh intervals. Internally, the intervals record changes of dune morphology and orientation, correlatable to wind fluctuations at multiple temporal scales. The basal Gleann Beag interval comprises compound cross-strata, deposited by oblique compound dunes. These dunes record a bimodal wind regime, resulting in net sediment transport toward the north. The Ladder interval records a reversal of sediment transport to the south, where straight-crested simple-dunes shaped by a seasonally variable winds formed. Finally, the Edinburgh interval records sediment transport to the west, where a unimodal wind formed sinuous-crested simple dunes. These observations demonstrate active and variable atmospheric circulation in Gale crater during the accumulation of the Stimson dune field, at multiple temporal scales from seasonally driven winds to much longer time-frames, during the Hesperian. These observations can be used to further understand ancient atmospheric conditions and processes, at a high temporal resolution on Mars.

Journal of Geophysical Research - Planets↗

USGS2000

Morphology and acoustic character of the Antarctic Wilkes Land turbidite systems: Ice-sheet-sourced versus river-sourced fans

The Wilkes Land continental slope contains an intricate network of submarine canyons that on the continental rise develop into a series of channel and overbank deposits of turbidite systems. We can define upper-fan, middle-fan, and lower-fan provinces. The Wilkes Land upper fans are characterized by large channels with relief up to 900 m, distances between levee crests up to 18 km, and channel-floor widths up to 6 km. Middle-fan channels also have high relief (∼300 m), and locally, interchannel areas exhibit mounded contourite-style deposits with high relief (up to 490 m). Within middle-fan sediment mounds there are acoustic facies of channel-overbank deposits from turbidity currents, and of sediment waves from contour-current sedimentation. The lower rise is characterized by small, shallow channels (50-75 m relief) and by interchannel areas of low relief, both characteristic of a lower-fan environment. The Wilkes Land turbidite systems show the following significant morphological differences compared to most river-sourced fans: (1) multiple large tributary channels across the upper and middle fan, (2) channel relief several times greater (900 m) than typical relief (100-200 m) for channels on fans less than 300 km in diameter, and (3) steep middle-fan and lower-fan gradients. We interpret the differences in channel network patterns, channel size, and middle-fan and lower-fan gradients between the Wilkes Land fans and other fans to result from the continental ice sheet feeding glacial ice streams that reached the outer continental shelf at times of glacial maxima. The Wilkes Land canyon-channel network patterns are comparable with the high-latitude Laurentian Fan and Labrador Sea channels. The Laurentian Fan also has large upper-fan channels with larger relief (800 m) than typical relief (200-300 m) expected for fans that are 600 km in diameter. Both the Labrador Sea and Laurentian Fan are fed by continental ice sheets at the shelf edge.

Journal of Sedimentary Research↗

USGS2012

Morphological evidence for discrete stocks of yellow perch in Lake Erie

Identification and management of unique stocks of exploited fish species are high-priority management goals in the Laurentian Great Lakes. We analyzed whole-body morphometrics of 1430 yellow perch Perca flavescens captured during 2007–2009 from seven known spawning areas in Lake Erie to determine if morphometrics vary among sites and management units to assist in identification of spawning stocks of this heavily exploited species. Truss-based morphometrics (n = 21 measurements) were analyzed using principal component analysis followed by ANOVA of the first three principal components to determine whether yellow perch from the several sampling sites varied morphometrically. Duncan's multiple range test was used to determine which sites differed from one another to test whether morphometrics varied at scales finer than management unit. Morphometrics varied significantly among sites and annually, but differences among sites were much greater. Sites within the same management unit typically differed significantly from one another, indicating morphometric variation at a scale finer than management unit. These results are largely congruent with recently-published studies on genetic variation of yellow perch from many of the same sampling sites. Thus, our results provide additional evidence that there are discrete stocks of yellow perch in Lake Erie and that management units likely comprise multiple stocks.

Lake Erie↗

USGS2018

Salt marsh loss affects tides and sediment budget in shallow bays

The current paradigm is that salt marshes and their important ecosystem services are threatened by global climate change; indeed, large marsh losses have been documented worldwide. Morphological changes associated with salt marsh erosion are expected to influence the hydrodynamics and sediment dynamics of coastal systems. Here the influence of salt marsh erosion on the tidal hydrodynamics and sediment storage capability of shallow bays is investigated. Hydrodynamics, sediment transport, and vegetation dynamics are simulated using the numerical framework Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport in the Barnegat Bay‐Little Egg Harbor system, USA. We show that salt marsh erosion influences the propagation of tides into back‐barrier basins, reducing the periodic inundation and sediment delivery to marsh platforms. As salt marshes erode, the sediment trapping potential of marsh platforms decreases exponentially. In this test case, up to 50% of the sediment mass trapped by vegetation is lost once a quarter of the marsh area is eroded. Similarly, without salt marshes the sediment budget of the entire bay significantly declines. Therefore, a positive feedback might be triggered such that as the salt marsh retreats the sediment storage capacity of the system declines, which could in turn further exacerbate marsh degradation.

New Jersey↗

USGS2018

Variation in DNA methylation is associated with migratory phenotypes of lake sturgeon (Acipenser fulvescens) in the St. Clair River

Lake sturgeon populations show a variety of movement patterns, but this variation is poorly understood. To compare two migratory phenotypes of lake sturgeon in the St. Clair River, multiple data types were analyzed. Individual fish were classified into migratory phenotypes based on acoustic telemetry data from 2012-2015. Lake sturgeon consistently showed movement from the St. Clair River upriver into Lake Huron or downriver into Lake St. Clair. The two migratory phenotypes were then compared for differences in morphometrics, genetics, and epigenetics. Morphological differences based on linear measurements were not detected between phenotypes. Microsatellite data from 11 loci suggested one population with no genetic differentiation between migratory phenotypes. Our epigenetic results indicated that the migratory phenotypes are differentially methylated (P=0.036), thus epigenetics may be associated with migratory differences in lake sturgeon. Only one restriction site was identified to be driving the differential methylation (P=0.012). While little evidence at neutral loci occurred for genetic differentiation of lake sturgeon, DNA methylation may play a role in the observed movement pattern variation. When combined with microsatellite and morphometric analyses, our results suggested that different migratory patterns may reflect phenotypic plasticity, allowing lake sturgeon to acclimate to short-term environmental variability. Without an integrated approach, the role of epigenetics in the migratory phenotype of lake sturgeon may have been overlooked. Further characterization of migratory phenotypes could be important for management to conserve behavioral variation across the distribution of lake sturgeon and for design of stocking guidelines.

Michigan↗

USGS2023

Sexual dimorphism in endangered Jemez Mountains Salamanders (Plethodon neomexicanus)

Sex ratio is a key demographic characteristic indicative of the condition of populations. Despite over 70 yr of study, researchers have not fully evaluated morphological characteristics that differentiate sex in Jemez Mountains Salamanders ( Plethodon neomexicanus ; federally endangered). Populations of this endemic salamander, which are distributed in north-central New Mexico, have undergone declines in the past two decades. We assessed morphological characters of 160 preserved P. neomexicanus specimens, evaluated our ability to infer sex in the field, and tested our ability to determine sex on a subset of preserved specimens. In preserved salamanders with body length (i.e., postcloaca snout–vent length, SVLp) ≥ 55 mm, females exhibited greater total length, trunk length, tail length, and cloaca length, and males exhibited greater precloacal tail width, head length, head width, and head height. We documented weakly female-biased size dimorphism. Females with SVLp ≥ 52 mm had cloacal rugae, whereas males with SVLp ≥ 51 mm had distinct papillose tissue in the cloaca and a cloacal cleft. In an evaluation of 30 preserved specimens, we correctly inferred sex in 97% of salamanders by cloacal characters alone. Of 29 adult salamanders captured in the field, we confidently inferred the sex of 27 individuals (16 females, 11 males) with SVL ≥ 44 mm. Thus, sex of most individuals can be correctly inferred in the field by cloacal characters. This information will aid researchers in better understanding population trajectories of this endangered species.

Journal of Herpetology↗

USGS2021

Sexual dimorphism in morphology and plumage of endangered Yuma Ridgway’s Rails: A model for documenting sex

Many applications in wildlife management require knowledge of the sex of individual animals. The Yuma Ridgway's rail Rallus obsoletus yumanensis is an endangered marsh bird with monomorphic plumage and secretive behaviors, thereby complicating sex determination in field studies. We collected morphometric measurements from 270 adult Yuma Ridgway's rails and quantified the plumage and mandible color of 91 of those individuals throughout their geographic range to evaluate intersexual differences in morphology and coloration. We genetically sexed a subset of adult Yuma Ridgway's rails ( n = 101) and used these individuals to determine the optimal combination of measurements (based on discriminant function analyses) to distinguish between sexes. Males averaged significantly larger than females in all measurements, and the optimal discriminant function contained whole leg, culmen, and tail measurements and classified correctly 97.8% (95% CI: 92.5–100.0%) of genetically sexed individuals. We used two additional functions that classified correctly ≥ 95.6% of genetically sexed Yuma Ridgway's rails to assign sex to individuals with missing measurements. These simple models provide managers and researchers with a practical tool to determine the sex of Yuma Ridgway's rails based on morphometric measurements. Although color measurements were not in the most accurate discriminant functions, we quantified subtle intersexual differences in the color of mandibles and greater coverts of Yuma Ridgway's rails. These results document sex-specific patterns in coloration that allow future researchers to test hypotheses to determine the mechanisms underlying sex-based differences in plumage coloration.

Arizona, California, Nevada↗

USGS2019

Discriminating among Pacific salmon, Rainbow Trout, and Atlantic Salmon species using common genetic screening methods

The five most common species of Pacific salmon, Rainbow Trout (steelhead) Oncorhynchus spp., and Atlantic Salmon Salmo salar intermingle in the North Pacific Ocean and its freshwater tributaries. Efficient morphological methods for distinguishing among these species are sometimes limited by condition of the specimen (degraded or missing morphology), life history stage, or training of the observer. Researchers have successfully applied various genetic methods to distinguish among these species when morphological analyses are not possible, but they cannot easily incorporate these methods into standard fish and wildlife population monitoring analysis workflows. Here we test five 5′–3′ exonuclease (TaqMan) assays developed from mitochondrial genes and provide novel methods that take advantage of TaqMan output to distinguish among these species. We found that combinations of as few as two of the five assays were adequate to distinguish all species. TaqMan chemistry is designed to interrogate a single nucleotide locus. We also explore the basis for the variation in the observed scatter plot distributions (variation in florescent signals) and show that this variation is due to nucleotide diversity in and near the probe site. Because the SNPs underlying the assays developed here are all physically close to one another along the mitochondrial genome, the potential exists to develop a single DNA sequence-based assay to discriminate among salmon species. This single assay can be added to a genotyping-by-sequencing panel to identify and exclude nontarget species from analyses.

Journal of Fish and Wildlife Management↗

USGS1964

Morphologic studies of the brachiopod genus Composita

The genus Composita consists of smooth-shelled athyroid brachiopods which in North America have a range from Late Devonian or Early Mississippian to Permian. Morphologic variation in the genus has been recognized by earlier workers, but few have tried to show exact relationships among the various forms. The present writers have attempted to trace the development of the genus through geologic time. Only North American species and varieties of Composita are treated in this paper. Forty-two species and varieties are included in a phylogenetic history of the genus. Nine other species are listed as doubtful forms. Eighteen specific and varietal names are rejected by the writers as obsolete. Morphologic intergradation among associated, synchronous forms is studied with the aid of frequency polygons. Lack of clear separation of the associated species within different maxima of the polygons indicates their dominant intergradation. These forms, previously described qualitatively, are regarded as typological species. A statistical method is used to test for differences between collections containing the same typological species. Significant differences in the slopes of reduced major axes are obtained in length-width, length-depth and depth-width plots of two collections containing Composita subtilita and Composita argentea . Significant differences also are obtained when two collections of Composita subtilita , Composita ovata and Composita elongata are compared in the same way. In spite of these results, slight nomenclatural changes are thought to be unnecessary. Use of the triangular graph as a means of distinguishing vertical subspecies is also tested. Four collections are plotted on one graph and five artificially separated groups of Composita subtilita on another. Mixed results are obtained. The method is suspect because the results are found to depend largely on the number of specimens used.

Journal of Paleontology↗

USGS2020

Subspecies differentiation in an enigmatic chaparral shrub species

Premise Delimiting biodiversity units is difficult in organisms in which differentiation is obscured by hybridization, plasticity, and other factors that blur phenotypic boundaries. Such work is more complicated when the focal units are subspecies, the definition of which has not been broadly explored in the era of modern genetic methods. Eastwood manzanita ( Arctostaphylos glandulosa Eastw.) is a widely distributed and morphologically complex chaparral shrub species with much subspecific variation, which has proven challenging to categorize. Currently 10 subspecies are recognized, however, many of them are not geographically segregated, and morphological intermediates are common. Subspecies delimitation is of particular importance in this species because two of the subspecies are rare. The goal of this study was to apply an evolutionary definition of “subspecies” to characterize structure within Eastwood manzanita. Methods We used publicly available geospatial environmental data and reduced‐representation genome sequencing to characterize environmental and genetic differentiation among subspecies. In addition, we tested whether subspecies could be differentiated by environmentally associated genetic variation. Results Our analyses do not show genetic differentiation among subspecies of Eastwood manzanita, with the exception of one of the two rare subspecies. In addition, our environmental analyses did not show ecological differentiation, though limitations of the analysis prevent strong conclusions. Conclusions Genetic structure within Eastwood manzanita does not correspond to current subspecies circumscriptions, but rather reflects geographic distribution. Our study suggests that subspecies concepts need to be reconsidered in long‐lived plant species, especially in the age of next‐generation sequencing.

American Journal of Botany↗

USGS2022

Development, structure, and behavior of a perched lava channel at Kīlauea Volcano, Hawaiʻi, during 2007

Channelized lava flows are commonly produced during the early stages of basaltic eruptions. These channels usually maintain their morphology until the eruption ends or discharge is diverted. In some instances, narrower channels can roof over, developing into lava tubes. We report here on a channelized flow erupted at Kīlauea volcano in 2007 that evolved into a “perched lava channel” composed of a string of interconnected, elongate lava pools, forming a lava channel/lava pool hybrid. The lava channel, which had a time-averaged discharge rate of ~3–9 m 3 /s, initially fed a series of flow branches that exhibited cooling-limited and volume-limited controls on flow length, sometimes with each process controlling a different morphological aspect of a single flow branch. The perched lava channel grew vertically primarily by overplating of the channel levees from frequent overflows, forming a compound flow field. This vertical growth only occurred when the distal end of the channel was blocked. When levee failure at the distal end of the channel caused the lava level in the channel to drop below the levee rim, no vertical growth occurred. Seeps of spiny lava and slabby pāhoehoe were common, erupting from uplift scarps on the channel levees, apparently fed by sills from denser, relatively crystal-rich material filling the bottom of the channel. We infer that lava in the channel was stratified in vesicularity and velocity, with foamy, vesicular, faster-moving lava at the top of the lava stream and denser, relatively outgassed, slower-moving lava filling the bottom of the channel. The channel levees were unstable, failing on several occasions, perhaps triggered by the levee seeps. The appearance of seeps, therefore, is one way of assessing the collapse potential of similar perched lava structures.

Hawaii↗

USGS2016

Challenge to the model of lake charr evolution: Shallow- and deep-water morphs exist within a small postglacial lake

All examples of lake charr ( Salvelinus namaycush ) diversity occur within the largest, deepest lakes of North America (i.e. > 2000 km 2 ). We report here Rush Lake (1.3 km 2 ) as the first example of a small lake with two lake charr morphs (lean and huronicus). Morphology, diet, life history, and genetics were examined to demonstrate the existence of morphs and determine the potential influence of evolutionary processes that led to their formation or maintenance. Results showed that the huronicus morph, caught in deep-water, had a deeper body, smaller head and jaws, higher eye position, greater buoyancy, and deeper peduncle than the shallow-water lean morph. Huronicus grew slower to a smaller adult size, and had an older mean age than the lean morph. Genetic comparisons showed low genetic divergence between morphs, indicating incomplete reproductive isolation. Phenotypic plasticity and differences in habitat use between deep and shallow waters associated with variation in foraging opportunities seems to have been sufficient to maintain the two morphs, demonstrating their important roles in resource polymorphism. Rush Lake expands previous explanations for lake charr intraspecific diversity, from large to small lakes and from reproductive isolation to the presence of gene flow associated with strong ecological drivers.

Biological Journal of the Linnean Society↗