Bedrock Outcrops Research Articles

“Process‐based similarity” revealed by discharge‐dependent relative submergence dynamics of thousands of large bed elements

AbstractRelative submergence of macroroughness elements such as boulders and bedrock outcrops, or large bed elements (LBEs), collectively, is a primary control on hydraulics and morphodynamics in steep, coarse‐bedded rivers. However, in practice, the property is typically represented by singular, often reach‐ or cross‐section‐averaged values that mask bed‐surface heterogeneity and joint distributions of local flow depths. By coupling sub‐meter resolution two‐dimensional (2D) hydrodynamic modeling with spatially explicit mapping of LBEs from a 13.2 km segment of a boulder‐bedded mountain river, we present complete distributions of LBE relative submergences at multiple spatial scales and explore their dynamism across discharges. Through distribution fitting and statistical analysis of resultant discharge‐dependent LBE relative submergence datasets, it was confirmed that segment‐ and reach‐scale datasets exhibited similar statistical properties and were able to be drawn from the same type of distribution. Further, the rate at which statistical and parametric properties changed between discharge‐dependent datasets were statistically equivalent between spatial domains, which we term “process‐based similarity”. Commonality in distribution type and the uniform between discharge–scaling relationships suggest mutual self‐organizing processes associated with the size‐frequency distribution, spatial arrangement, and submergence of LBEs were present between most domains.

Creep leakage process of remaining soils in near-surface fissures in a karst area with bedrock outcrops

As a global ecological environmental problem, rocky desertification is derived from the exposure of large areas of bare rock on slopes, and soil remains only between rock exposures and in fissures. These remaining soils are crucial to vegetation growth and the amelioration of rocky desertification, but they are prone to leakage loss. This study aimed to reveal soil creep displacement (SCD) and the characteristics, process and mechanism of soil particle leakage in fissures on sloping land in karst areas. Six fissures on the karst plateau of Guizhou were studied by paint marking and soil particle analysis techniques, and SCD was monitored during three rainfall periods (cumulative rainfall of 104.5, 151.2 and 332.7 mm). The results showed that for 104.5 mm of rainfall, the SCD of the fissures was 1.0 ∼ 2.5 cm and accounted for more than 62.5% of the displacement observed after a total of 332.7 mm of precipitation. Additionally, the SCD was 0.2 ∼ 0.3 cm at 181.5 mm of rainfall. Therefore, rainstorms or downpours are a key factor driving soil fissure leakage, and the leakage form is mainly soil creep. Under three rainfall observation periods, the particle content with different particle sizes at soil-rock interfaces and soils in six fissures showed that fissure soils do not show uniform downward leakage; instead, some particles in the soil layers or at soil-rock interfaces randomly leak to lower layers during the process of creep leakage loss. Hence, the occurrence of soil layers and particles is random, and the soil particles at the soil-rock interfaces and in soil layers in fissures may leak downward. The results indicate that soil creep leakage in fissures is a complex process that depends on both internal factors and external factors (such as rainfall).

OSL‐14C‐10Be: A novel composite geochronometer for simultaneous quantification of timing and magnitude of change in bedrock outcrop erosion rate

AbstractQuantifying past changes in erosion rate is essential for deciphering earth surface processes and their driving mechanisms. Coupledin situcosmogenic14C‐10Be has been shown to be a useful chronometer in detecting changes in erosion rate, but its detection ability is limited to rapidly eroding fluvial landscapes and changes greater than a factor of two; and in any case, it cannot uniquely quantify both the magnitude and the timing of change in erosion rate. Here, we establish a theoretical framework to show that this limitation can be overcome by combining the recently developed optically stimulated luminescence (OSL) rock surface exposure dating with the14C‐10Be chronometer. We demonstrate that the resulting OSL‐14C‐10Be composite geochronometer can determine both the magnitude and the timing of an abrupt change in bedrock erosion rate by a factor of < 0.8 or > 1.2 over 100–104a timescales, where erosion rates are < 10−2 cm a−1.

Bedrock outcrops weakly promote rather than inhibit soil carbon sequestration after vegetation restoration

Vegetation restoration can increase soil carbon (C) content in karst regions characterized by highly exposed carbonate rocks; however, it remains unclear whether and how bedrock outcrops contribute to soil C-accumulation after vegetation restoration. We aimed to investigate the magnitude and mechanisms of bedrock outcrops on soil C-accumulation after vegetation restoration. Here, we selected 362 fixed locations to investigate changes in soil organic carbon (SOC) content and density before and after cropland restoration in a karst catchment with varying bedrock exposure ratios and initial soil C pools prior to restoration. Active vegetation restoration (i.e., cropland converted to forage grass, plantation forest, and a combination of grass and forest) and natural regeneration (cropland abandoned) were compared, with croplands maintained with no change as the control. Compared to croplands maintained with no change, SOC density significantly increased in the four vegetation restoration types. The SOC accumulation rate was higher for natural regeneration (39 g C m−2 yr−1) than for the three active restoration strategies (18–27 g C m−2 yr−1). SOC accumulation decreased with a higher initial pool size of soil C but increased with nitrogen accumulation and soil exchangeable calcium (Ca2+) concentration. Higher bedrock outcrops reduced soil volume but increased SOC content through their indirect effects on the initial pool size of soil C, external nitrogen inputs, and soil Ca2+ concentration. This weakly promoted rather than inhibited SOC sequestration. Our findings highlight the effectiveness of various restoration strategies in promoting SOC accumulation in karst areas, as well as the need to take bedrock outcrops and initial soil C pools into consideration when modeling SOC dynamics and maximizing C sinks for vegetation restoration.

Metamorphic bedrock geometry of Santorini using HVSR information and geophysical modeling of ambient noise and active-source surface-wave data

Santorini is the most active volcano of the Southern Aegean Volcanic Arc, with volcanic material that has accumulated during the last 600+ Kyrs on top of the pre-volcanic Santorini island. The geometry of the pre-volcanic basement not only provides constraints on the volcanic history, but is also fundamental for seismic hazard assessment, as it partly controls site-effects on strong ground motions. We investigate the geometry of the metamorphic (Cycladic) basement of Santorini using information from both passive (noise) and active source data. We performed a large number (∼280) of single-station ambient noise measurements and collected additional data from 42 previous studies to compute the Horizontal-to-Vertical Spectral Ratio (HVSR) curves. The majority of the recovered HVSR curves show prominent spectral ratio peaks (locally larger than 7–8) indicating a large impedance contrast between pyroclastic volcanic strata and bedrock metamorphic formations. We also performed active (MASW) and passive (Noise Array) surface wave measurements at 4 selected sites to determine local dispersion curves. To find the 1D Vs structure from the surface down to the metamorphic bedrock we performed a joint Monte Carlo inversion of the dispersion curves and the fundamental frequency (f0HVSR) values from the HVSR curves. These models, as well as deep borehole information and HVSR data along the caldera cliff, where the thickness and stratigraphy of the volcanic formations above the bedrock can be directly observed, allowed us to determine a linear relationship between the thickness of the pyroclastic formations and their fundamental resonance period for central-southern Santorini. The resulting geometry of pre-volcanic island shows deep basins around the pre-Alpine bedrock outcrop (Profitis Ilias) and generally agrees with recent results from larger-scale tomographic and gravity data but with some significant local differences. The basins are 200+ meters thick in the Kamari and Perissa area (southeastern Santorini) and >400 m thick in the central (Fira-Imerovigli) area, while there is a thick (∼70-130 m) pyroclastic layer on top of a metamorphic basement “plateau” in the Megalochori area.

3D shear-wave velocity structure for Oran city, northwestern Algeria, from inversion of ambient vibration single-station and array measurements

The city of Oran experienced several earthquakes. Therefore, the characterization of its subsurface is crucial for a better evaluation of the seismic hazard. Using ambient vibration single-station and array measurements at 193 sites, the HVSR curves showed a variation of the fundamental frequency peak between 0.3 and 7.4 Hz, growing towards the west, with maximum amplitude of ∼6. The shallow structure has been explored by means of F–K analysis. Joint inversion of the HVSR and Rayleigh wave dispersion curves showed 3 layers of soft and stiff sediments of varying thicknesses overlying the bedrock. The shear-wave velocity (Vs) of the sediments varies between 280 and 1300 m/s and that of the bedrock can reach 2500 m/s. Cross sections show a decrease in sediments thickness from east to west where bedrock outcrops. The maximum depth of bedrock is 1050 m northeast of the city. The obtained Vs models support a soil classification ranging from stiff soil to hard rock.

Active Ground Patterns Near Mars' Equator in the Glen Torridon Region of Gale Crater

AbstractOn Mars, near the equator, much of the terrain in Gale Crater consists of bedrock outcrops separated by relatively smooth, uniform regolith surfaces. In scattered sites, however, distinct patterns—in the form and texture of the ground surface—contrast sharply with the typical terrain and with eolian bedforms. This paper focuses on these diverse, intriguing ground patterns. They include ∼1 to >10 m‐long linear disruptions of uniform regolith surfaces, alignments, and other arrangements of similar‐sized rock fragments and shallow, ∼0.1 m‐wide sandy troughs 1–10 m in length. Similar features were recognized early in the Mars Science Laboratory (MSL) mission, but they received only limited attention until Curiosity, the MSL rover, encountered striking examples in the Glen Torridon region. Herein, the ground patterns are illustrated with rover images. Potential mechanisms are briefly discussed in the context of the bedrock composition and atmospheric conditions documented by Curiosity. The evidence suggests that the patterns are active forms of spontaneous granular organization. It leads to the hypothesis that the patterns arise and develop from miniscule, inferred cyclic expansion and contraction of the bedrock and regolith, likely driven by oscillating transfers of energy and moisture between the atmosphere and the terrain. The hypothesis has significant implications for studies of contemporary processes on Mars on both sides of the atmosphere‐lithosphere interface. The ground patterns, as well as ripples and dunes formed by the wind, constitute remarkable extra‐terrestrial examples of granular self‐organization, complex phenomena well known in diverse systems on Earth.

Phytocoenotical behaviour of nemoral and boreal-nemoral plant species in taiga zone communities

Phytocoenotic behaviour of 14 nemoral or boreal-nemoral vascular plant species is analyzed in the middle- and southern-taiga subzones in comparison with that in the broadleaved-forest zone, based upon the set of 1669 relevés made in European Russia in 1996–2018. The nemoral species are mainly represented by shadow mesoeutrophic plants from the “corteges” of Tilia cordata s. l. and Fagus sylvatica. The more light-demanding plants from the Quercus robur “cortege”, either mesotrophic, or mesoeutrophic, more often demonstrate the boreal-nemoral type of zonal distribution. In the boreal-forest zone, linden and beech companions are typical for the southern-boreal nemoral-herb / sorrel spruce (Picea abies s. l.) forests on placors as well as the valley / riparian tall-herb forests, including the middle-boreal ones. The oak companions also inhabit grass-feathermoss pine (Pinus sylvestris) forests, besides the spruce forest types mentioned. Species from all the named “corteges” are also common in the small-leaved forests. The Betula companions which grow together with the nemoral plants in boreal forests could also be subdivided into the two florogenetical groups, namely a) the boreal, originally subalpine plants and b) the boreal-nemoral ones, originally oak companions. Species from the latter group often become widespread and dominant in the small-leaved forests; a good example is provided by Aegopodium podagraria. The rank correlation (Spearman rS) analysis shows the projective cover increase is connected with either the growing season warmth supply, or the climate oceanicity for both nemoral and boreal-nemoral species. These effects are most sound in the placor community sequence from broadleaved forests to sorrel and then bilberry-feathermoss spruce ones but weakened in the tall-herb forests on rich soil and completely levelled in the aspen (Populus tremula) forests. Carbonate bedrock outcrops contribute to nemoral species survival in the areas they inhabited during the climatically favourable epochs; they also favoured the migration of these species during the interglacials. Individualization of coenotic patterns of nemoral species at their distribution limits does not contradict to joint occurrence of such plants in relict / extrazonal locations.

Rock slope failure in the Southern Carpathians (Romania): Range-wide inventory and links with long-term mountain landscape evolution

Rock slope failure (RSF) is now widely recognised as a significant contributor to the denudation of mountain ranges. Its spatial incidence can consequently be a valuable indicator of prevailing process domains, tectonic regimes and climatic variations, whether active or past. Here we provide the first systematic inventory of RSF in the Southern Carpathians, a mountain range marginally glaciated during the Pleistocene, cut by valleys up to 1.3 km deep, and displaying low-gradient summit erosion surfaces that suggest late Neogene uplift and incision of an extensive plateau. We discuss the spatial distribution of RSF in terms of process interactions and landscape evolution scenarios. Widespread metamorphic bedrock outcrops are confirmed as highly susceptible to RSF, particularly to large-scale slope deformation, but RSF also occurs on other lithologies as smaller rockslides and avalanches. Substantial spatial densities of RSF cluster around the residual, plateau-like range-top surface rims. We ascribe this to the ‘raised plateau’ features of the mountain range, where its fat, flat massifs engender greater slope stresses than would thin, serrated ones where arêtes and pyramidal peaks are gravitationally more stable. A large minority (42 %) of RSFs are spatially associated with glacial cirques and trough flanks. While these nominally qualify as paraglacial RSFs, glacial erosion may not be the main driver because the majority of RSFs occur along ridgetops and upper hillslopes in previously unglaciated fluvial contexts. Many of them thus qualify as parafluvial RSFs – i.e., occurring within a fluvial catchment but not directly generated by stream undercutting. We introduce the concept of fluvial–parafluvial and periglacial–parafluvial cycles as complementary to the recognised glacial–paraglacial cycle. All three process regimes may have prevailed concurrently or in succession, emphasising that cirque glaciation was probably not a principal agent in shrinking range-top erosion surfaces during the Quaternary. We point to post-orogenic (Neogene) tectonic uplift as the overarching driver of RSF in the Southern Carpathians, with pervasive fluvial incision keeping slopes close to failure thresholds. The role of RSF (extant and in earlier cycles) as a primary agent in perimeter scarp retreat and massif dissection here offers a ‘Transylvanian model’ of global interest whether as a comparator or a contrast for other ranges.

Scale dependent spatial structuring of mountain river large bed elements maximizes flow resistance

Macro-roughness elements such as boulders and bedrock outcrops, collectively referred to as large bed elements (LBEs), are key features influencing hydrodynamics and morphodynamics in mountain rivers. Where LBEs are abundant and account for a substantial portion of total flow resistance, existing geomorphic theory, previous physical experiments, and limited field observations support the theory that LBE configurations adjust to maximize flow resistance. However, methods to explicitly map individual features along entire river segments are lacking, thus limiting analysis of LBE spatial structure in boulder-bedded rivers. In addressing these gaps, this study sought to develop a procedure for mapping LBEs from 3D point-clouds, explore LBE spatial structure in a real boulder-bedded river, and test the hypothesis that LBE configurations were organized to maximize flow resistance. The mapping procedure applied a ground classification algorithm to produce a roughness surface model, from which LBEs were extracted by a marker controlled watershed algorithm. Implementing the procedure, 42,176 LBEs were mapped in 13.2-km of the mountainous Yuba River (Northern California). Scale and discharge-dependent LBE concentration and spacing metrics were quantified for multiple laterally and/or hierarchically nested spatial domains and classified to differentiate three flow-resistance based hydrodynamic regimes: isolated roughness, wake interference, and skimming flow. Of these regimes, wake interference corresponds to a state of maximum resistance, so hypothesis testing involved determining if this regime was dominant. Results confirmed 25 of 28 segment- and reach-scale LBE concentrations were in the wake interference regime. However, spacing metrics classified 24 of these same spatial domains in the skimming flow regime. Concentration metrics, which quantify LBE density in a given spatial area, differ from spacing metrics, which represent LBE proximity to one another. While comparison of segment and reach-scale regime classifications by each metric concluded concentration was superior to spacing for regime classification purposes, these disparities leave open questions about this extremal model of geomorphic adjustment. Lastly, lateral variability of metrics across the river corridor had implications for discharge-dependent resistance.

A morphological classification of coastal forelands, with examples from South Africa

Alongshore variations in the cross-shore width, and therefore volume, of sandy beaches are important because these reflect spatial variability in the operation of wave- and wind-driven processes taking place both at the shoreface and in the supratidal zone. One key geomorphic signature of variations in cross-shore beach width is the development of coastal forelands. Different foreland types have been described in the literature from very specific geomorphic contexts, but hitherto there has been no overarching classification scheme that genetically links these different foreland types, or considers them in the wider context of sandy beach dynamics. In order to achieve this aim, this study maps and inventorises 87 forelands from the South African coast (~2600 km long), and classifies these into four morphological types: salients, tombolos, cuspate forelands, and ramp forelands. These foreland types have different morphological properties, reflecting the interplay of coastal erosional and depositional processes and any antecedent conditions; and a varying balance of morphodynamic controls on their development and behaviour. These include variations in wave (and to a lesser extent wind) energy, sediment supply, and the presence of bedrock outcrops of different sizes, shapes and positions along the shoreline. Analysis of foreland morphology and dynamic behaviour, based on examples from South Africa, enables a better understanding of coastal forelands globally as integrated sediment systems and responsive to the range of forcings driving coastal change.

Permafrost-based geomorphology of the Mt. Foscagno - Mt. Forcellina ridge (Adda – Inn River basins, Central Italian Alps)

ABSTRACT The permafrost-based geomorphological map of the Mt. Foscagno – Mt Forcellina ridge (Central Italian Alps) shows the distribution of permafrost probability (high, medium, low probability, and probable absence) obtained by the application of PERMACLIM (Guglielmin et al., 2003), a GIS-based model integrating Digital Elevation Model (DEM) topographic data and the Climatic DataBase (CDB) available from Automatic Weather Stations (AWS). In addition, the map provides information on the outcropping bedrock, the genesis and grain size of near-surface deposits, and geomorphological features with particular reference to periglacial and glacial landforms. Moreover, the map represents locations and values of ground measurements, Bottom Temperature of winter Snow cover (BTS) and Vertical Electric Soundings (VES), and the Mean Annual Air Temperature (MAAT; Guglielmin et al., 2003).

Numerical analysis of midwinter infiltration along the soil-rock interface: A pathway for enhanced bedrock recharge

Shallow bedrock aquifers are prevalent across the Northern Hemisphere and can be the primary source of freshwater for many communities. Cryospheric impacts from climate warming are particularly concerning for bedrock aquifers where recharge is dominated by winter precipitation. For the management and protection of fractured rock groundwater supplies, the processes influencing infiltration and recharge under warmer winter conditions require a greater understanding. As such, a numerical investigation was undertaken with the objective of testing a conceptual model of midwinter infiltration and recharge near a granitic Canadian Shield bedrock outcrop using data collected over an unseasonably warm and rainy winter in eastern Ontario, Canada. Additional objectives were to determine if infiltration and recharge would be limited through frozen soils without an outcrop and to explore the hydrologic implications of an additional midwinter snowmelt event. Results supported the concept that outcrops provide preferential infiltration along the soil-rock interface at outcrop margins, which enables localized bedrock recharge under frozen conditions. To simulate soil moisture content near the outcrop, bedrock runoff was needed as additional lateral input in the lower soil profile (75 cm). The amount of runoff required as input was controlled by the hydraulic conductivity of the soil-rock interface. In the absence of an outcrop, limited midwinter infiltration occurs due to reduced permeabilities of frozen soils from repeated early winter rainfall and snowmelt events. Additional midwinter melt events can likely increase bedrock recharge, but the associated decline in snow depth deepens soil frost which delays further infiltration and increases surface runoff. Simulations suggest winter is becoming a more active time for bedrock recharge where outcrops are present, but wetter conditions have implications for frozen soil permeability. Findings extend to similar seasonally frozen bedrock environments which are relied on as a source of freshwater and are rapidly changing under a warming climate.

Sensitivity analysis of input ground motion on surface motion parameters in high seismic regions: a case of Bhutan Himalaya

Abstract. Historical earthquakes demonstrate that strong motion characteristics and local soil condition, when coupled, significantly influence seismic site response. Interestingly, most of the Himalayan earthquakes depicted anomalous behavior per the site conditions historically. Being one of the most active seismic regions on earth, the eastern fringe of the Himalaya has observed many devastating earthquakes together with non-uniform damage scenarios. To quantify such anomalies, we evaluate surface motion parameters for a soft soil deposit located in the city of Phuentsholing in western Bhutan. Using one-dimensional site response analysis, the sensitivity of ground motion variation is estimated. This study accounts for the earthquakes of moment magnitudes 6.6 to 7.5 with a wide variation in peak ground acceleration (PGA). To dissect the characteristics of six inputted ground motions on eight local ground conditions, a sensitivity analysis is performed statistically. The statistical correlation of the response datasets and the linear regression model of the bedrock outcrop and the surface motion spectral acceleration along the stratified depth are examined to quantify the variation in surface motion parameters. The results highlight that the strong motions with PGA greater than 0.34 g demonstrate greater sensitivity, leading to some anomalies in response parameters, especially amplification. Similar results were obtained for the low PGA range (<0.1 g).

Classification of Coastal Belts on the Coral Coast of Viti Levu, Republic of Fiji, South Pacific, using the BCCS (Biophysical Cross-shore Classification System)

Finkl, C.W. and Makowski, C., 2022. Detailed interpretation of satellite images of coastal belts on the Coral Coast of Viti Levu, Republic of Fiji, South Pacific, using the BCCS (Biophysical Cross-shore Classification System). Journal of Coastal Research, 38(3), 491–511. Coconut Creek (Florida), ISSN 0749-0208. Lying on the southwest Fijian coast of Viti Levu, the Coral Coast is noted for its fringing coral reefs that extend for an overall alongshore length of about 80 km (from Momi to Suva), with the study area being a 32-km-long subset in the Sigatoka region. The fringing reefs, extending offshore for an average maximum distance of about 650 m, are broken into contiguous segments by deep-water cross-shore channels composing discrete coastal belts. When the fringing reef segments are combined with other onshore (terrestrial) eco-geomorphological units, they make up nine distinct coastal belts in the study area comprised by 35 domains. The cross-shore classification of the Coral Coast examples was based on application of the BCCS (Biophysical Cross-shore Classification System), which required interpretation of satellite images to comprehend cross-shore catenary (linked) sequences that had alongshore extent. Imagery from 2010 to 2017 was accessed to obtain the best possible views of each reef segment and adjacent mountain hinterland. Due to spatial limitations, capabilities of the Google Earth Pro platform were accessed to acquire sufficient interpretive details for compilation of cross-shore transectal archetypes and subarchetypes from the reef front to coastal mountain slopes. Typical cross-shore classificatory sequences consisted of Coral Reef (Cr), Flat (F), Beach (Be), and Mountain (M) archetypes that formed tetrasequent Cr-F-Be-M catenas. Although a limited number of small Delta (De) archetypes overrode back-reef flat margins, their frequency of occurrence was not a domainal characteristic. The occurrence of Developed (Dv) archetypes were more or less ubiquitous onshore, whereas alongshore bedrock outcrops of the Rock (R) archetype were rare. Because the scale of natural and anthropogenic features along the coast demanded a detailed (hectometric) coastal classification, the BCCS was applied on an experimental basis to ascertain its applicability as an exemplar for similar studies in insular settings elsewhere.

Geologic and geomorphic evidence for multi-phase history of strands of the San Andreas fault through the San Gorgonio Pass structural knot, southern California

Abstract The San Gorgonio Pass region of southern California is a locus of extensive Quaternary deformation within a multi-strand section of the San Andreas fault zone. The geomorphology of the San Gorgonio Pass region reflects the complicated history of geologic events in the formation of this structurally complex region. We define fault-bounded blocks in San Gorgonio Pass and focus on two that are characterized by extensive crystalline bedrock outcrops with similar bedrock lithologies. These two blocks are separated by the San Bernardino strand of the San Andreas fault. Morphometric variables, including local relief, slope, slope distribution, and surface roughness, consistently demonstrate distinctions between the bedrock upland regions of the two blocks. Geologic observations of the region highlight differences in Quaternary units within the two blocks, reflective of the differing surficial processes active in each block. Within the Kitching Peak block, the morphology highlights a lineament that we informally name the Lion Canyon lineament. This boundary more clearly differentiates the two regions, as compared to the mapped San Bernardino strand, and may represent the previously active strand or bounding structure in this section. The distinction in morphology and surficial processes leads to our interpretation that the Kitching Peak and Pisgah Peak blocks have experienced different uplift histories. This further leads to the conclusion that the San Bernardino strand, broadly defined, has been integrated, at some point in the past, with the Banning strand, allowing for through-going rupture along the fault system. This connectivity may have occurred along the Burro Flats section of the San Bernardino strand or the Lion Canyon lineament. The fault connection along the mapped trace of the San Bernardino strand is not currently evident at the surface, however, suggesting that the integration has been disrupted. We propose this is due to intervals of N-S compression in the region, manifest as slip along the San Gorgonio Pass fault zone and other regional faults. We present evidence for lateral displacement along the San Bernardino and Banning strands of the San Andreas fault, discuss the implications of these displacements, and propose a sequence of fault activity, including multiple phases of activity along the San Bernardino and Banning strand pathway to account for the structural complexity and lack of surficial fault continuity.

New approaches to rock landform and landscape conservation

Rock landforms are natural outcrops of solid bedrock, exposed at the earth surface due to higher resistance to weathering and erosion. They are important carriers of information about past and more recent geological and geomorphological processes, underpin biodiversity and cultural values, and may have considerable aesthetic significance. Many are popular tourist destinations. They are subject to different threats, including physical damage through quarrying and vandalism, may suffer from excessive rock climbing, or their values are compromised by uncontrolled vegetation growth. Their interpretation is often poor or non-existent. Conservation measures and solutions are mainly site-specific and typically require coordination with biological conservation, including prioritization of conservation efforts focused on localities of special scientific significance.

Optimum intensity measures for probabilistic seismic demand model of subway stations with different burial depths

In this paper, optimum intensity measures for probabilistic seismic demand model of subway stations with different burial depths are investigated. A three-story three-span subway station which is commonly seen in the metro system in China, is selected as a typical case. The subway station is embedded in two generic engineering sites corresponding to site classes II and III specified in Chinese code for seismic design of urban rail transit structures. Five different burial depths (4 m, 8 m, 12 m, 16 m, and 20 m) are considered in this study. Nonlinear soil-structure interaction time history analyses are conducted on the two-dimensional numerical model of the subway station embedded in two different engineering sites. Based on the theory of wave propagation in homogeneous and elastic media, seismic excitations at the engineering bedrock for the two generic sites are back calculated from an ensemble of 50 pairs of as-recorded seismic motions at bedrock outcrop. The efficacy of twenty-one commonly-used scalar intensity measures (IMs) for seismic response prediction of underground structures are evaluated by the metrics of efficiency, practicality, proficiency and sufficiency. The numerical results reveal that for subway stations embedded in site class II, velocity spectrum intensity (VSI) is the optimum IM with different burial depths. Furthermore, for subway station embedded in site class III, VSI and peak ground velocity (PGV) are the optimum IMs with a burial depth of 4 m, and VSI and compound velocity-related intensity measure are the optimum IMs with burial depths of 8 m–20 m. Moreover, for the three well-recognized amplitude IMs, peak ground acceleration (PGA), PGV, peak ground displacement, with the increase of the burial depth of underground structures, the proficiency of PGV is gradually enhanced compared with PGA. Finally, based on the theory of one-dimensional wave propagation in homogeneous and elastic half-space, the preliminary mechanism explanation of the optimum amplitude IMs for variation of burial depth is given.

Skalne grzyby w Polsce i na świecie – terminologia, rozmieszczenie, poglądy na rozwój = Rock mushrooms in Poland and the world – terminology, distribution, views evolution

Various shapes are taken on by the bedrock outcrops emerging from regolith cover, typically described using the generic term ‘crag’ or ‘tor’. Consequently, specific terms have been proposed to account for this variety. Among these outcrops are those consisting of a narrow lower part (stem) and a wider upper part (cap), resembling a mushroom. In English, they are named pedestal rocks if built of hard, well-lithified rock; or hoodoos if the rock is softer, but there is no established boundary line between the two. Not uncommonly, however, and perhaps less formally, they are referred to as ‘rock mushrooms’ (or mushroom rocks), to emphasise the unusual shape. In Polish, the term equivalent to ‘rock mushroom’ has been used at least since the 1930s, and appears to be a legitimate part of geomorphological vocabulary. In this paper, we present the occurrences of rock mushrooms in different lithologies, identify geological controls and review various hypotheses regarding their origin and evolution. Rock mushrooms are known from various lithological settings, although some bedrock types clearly favour their origin more than the others. First of all, these are sandstones and aconglomerates. Rock mushrooms are up to 10 m high, whereas height proportions between the stem and the cap vary, resulting in a great variety of specific shapes, from large monoliths on low (<1 m) pedestals to tiny caps on top of slender stems >5 m high. In Poland, the north-eastern part of the Stołowe Mountains abounds in rock mushrooms developed in Upper Cretaceous sandstones; but they also occur in other parts of the Sudetes, where Cretaceous sandstones crop out; and in the flysch Carpathians. Specific variants of rock mushrooms in clastic rocks include those related to non-uniform silification of sandy sediments (e.g. Fontainebleau Forest, France) or secondary ferruginisation of sandstone beds (e.g. Kokořinsko, Czechia). Rock mushrooms are also known from limestone and dolomite terrain, with the massive forms in Ciudad Encantada, Spain, being probably the tallest known from literature. The latter are up to 15 m high and have developed within a dolomite succession. Heights above 10 m are also attained by rockmushrooms in the volcanic succession of Cappadocia, Turkey, locally described as ‘fairy chimneys’. A great variety of shapes are documented from this region, with conical caps being very common. Granite rock mushrooms are comparatively rare, and in this case a clear distinction between the stem and the cap usually proves difficult. More commonly, the outcrops assume a shape resembling the letter ‘S’ or ‘Ω’, with basal undercutting grading smoothly into a wider upper part. A specific term ‘flared slope’ has been proposed to account for this basal concavity. Finally, cap-on-stem situations typify eroded glacigenic deposits, best known from the Alps, where boulders embedded in till or outwash sediments provide a protective cap to the underlying mass. As the overall shape is often conical, the term ‘earth pyramid’ is used in some languages (e.g. Polish and German). Rock mushrooms have more than one origin, and many can in fact be polygenetic. In each case, however, rock disintegration is clearly more efficient in the basal part. The reasons for enhanced efficacy at this point vary, and include: (a) aeolian undercutting – this view prevails in primary and secondary geographical education, even as wind-abraded rock mushrooms are by no means the most common examples; (b) differential weathering related to lithological or structural heterogeneity of rock, even as the exact mechanisms of weathering may vary; (c) subsurface (subsoil) weathering (etching) leading to the origin of a narrow stem, subsequently exposed; (d) wave-undercutting in coastal settings; (e) overland flow and gully erosion – these processes are fundamental for rock-mushroom evolution in poorly-lithified deposits; (f) negative feedback between stress and erosion on exposed bedrock outcrops.

Environmental drivers of taxonomic and phylogenetic diversity patterns of plant communities in semi-arid steppe rangelands of North Africa

Since phytoecological and biodiversity studies deepen our understanding on ecosystem functioning and habitat health status of rangelands, this study analyzed the composition and plant taxonomic and phylogenetic diversity of semi-arid steppe vegetation communities in rangelands of northeastern Algeria. Based on 80 floristic samples, vegetation was analyzed using various species diversity parameters (incidence- and abundance-based diversity and similarity indices, rarefaction and extrapolation estimations). Sampling totaled 75,197 plant individuals that were classified into 63 species, 55 genera and 21 families, with predominance of Asteraceae (33.3%) and Fabaceae (14.3%) species. Rarefaction and extrapolation curves applied for the whole steppe vegetation showed that the expected species richness was stable and no rare species could be found when increasing the sample size. Generalized linear models showed that the variation of plant diversity parameters (alpha-biodiversity) was significant among the phytoecological groups individualized. The multiple factor analysis demonstrated that inter-relationships between the phytoecological groups result from characteristics of soil surface, vegetation indicators, and dominant plant species that influenced plant diversity indices. The qualitative and quantitative analysis of similarity (beta-biodiversity) revealed high resemblances (>50%) between these groups, indicating a spatial homogenization of plant communities, which are dominated by annual species. The variation of phylogenetic diversity, estimated using taxonomic structures (i.e. genus/species and family/species ratios) was related to local environmental conditions. Phylogenetic diversity increased with the increase in total vegetation cover and the average height of Halfa grass (Stipa tenacissima), but it was negatively correlated with land degradation indicators such as sand deposit sheets, bedrock outcrop, coarse-grained materials, and plant necromass or vegetation litter). This study demonstrated that despite the recorded plant diversity, the quality of rangelands in the study area was of a therophytic character (substantial level of annuals), indicating a state of land and vegetation degradation in rangelands of northeastern Algeria.