Glacial erosion and geomorphology in the northwest Sierra Nevada, CA

Pleistocene glacial erosion left a strong topographic imprint in the northwestern Sierra Nevada at many scales, yet the specific landforms and the processes that created them have not been previously documented in the region. In contrast, glaciation in the southern and central Sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the European Alps. This study describes glacially eroded features in the northwest Sierra and presents inferred linkages between erosional forms and Pleistocene glacial processes. Many relationships corroborate theoretical geomorphic principles. These include the occurrence of whalebacks in deep ice positions, roches moutonnées under thin ice, and occurrence of P-forms in low topographic positions where high subglacial meltwater pressures were likely. Some of the landforms described here have not previously been noted in the Sierra, including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice-marginal channels.     

Glacial erosion and relief production in the Eastern Sierra Nevada,California

The proposal that climate change can drive the uplift of mountain summits hinges on the requirement that glacial erosion significantly enhances the relief of a previously fluvially sculpted mountain range. We have tested this hypothesis through a systematic investigation of neighbouring glaciated and nonglaciated drainage basins on the eastern side of the Sierra Nevada, CA. We present a simple, objective method for investigating the relief structure of a drainage basin, which shows noticeable differences in the spatial distribution of relief between nonglaciated and glaciated basins. Glaciated basins on the eastern side of the Sierra Nevada have only ∼80 m greater mean geophysical relief than nonglaciated basins. This “extra” relief, though, is attributable principally to the larger size of the glaciated basins, as geophysical relief generally increases with basin size. The glaciers on this side of the range were only responsible for relief production if they substantially increased headward erosion rates into low relief topography, such as an elevated plateau, and thus enlarged previously fluvial basins. We carried out a preliminary morphometric analysis to elucidate the importance of this effect and found that the glaciers of the eastern Sierra Nevada may have eroded headward at considerably faster rates than rivers, but only when they were not obstructed from doing so by either competing larger glaciers in adjacent valleys or transfluent ice at the head of the basin. Our results also suggest that, in temperate regions, alpine glaciers are capable of eroding downward at faster rates than rivers above the equilibrium line altitude (ELA). Although we can rule out significant peak uplift in response to local relief production, in the special case of the Sierra Nevada the concentration of mass removal above the ELA could have contributed to flexural uplift at the edge of a tilting block.     

Patterns of mortality in Freetown,Sierra Leone

A demographic and spatial analysis of mortality in Freetown, Sierra Leone, is presented, with emphasis on data for the census years 1963 and 1974. Consideration is first given to the availability of data and their quality. The authors then examine geographic variations in mortality within the city, age- and sex-specific death rates, the major causes of death, and death certification.     

Transnational mining corporations and sustainable resource‐based livelihoods in Sierra Leone

This paper draws from world‐systems and sustainable livelihoods approaches to analyze the connections between multinational exports of rutile (titanium oxide), diminished ecological resources and resource‐based livelihoods, and gendered household dynamics in a peripheralized mining region in Sierra Leone. The discussion focuses on how the extraction of mineral resources instigated by exogenous capital investors forces links to household transformation, particularly the vulnerability context of women. Using archival records and field survey data, the case study of rutile mining in southwestern Sierra Leone connects the low‐waged mining labour of traditional resource‐based subsistence communities and deepening marginalization of and financial pressures on women in mining households to global mineral markets. The study focuses on women's coping mechanisms that are embedded within traditional social networks in relation to an external intervention, a low‐tech mechanical cassava grater, intended to strengthen their livelihoods. It finds that the potential for this transformation is impeded by sociocultural, environmental and financial limitations.     

EVIDENCES FROM HISTORICAL DOCUMENTS OF LANDSCAPE EVOLUTION AFTER LITTLE ICE AGE OF A MEDITERRANEAN HIGH MOUNTAIN AREA,SIERRA NEVADA,SPAIN (EIGHTEENTH TO TWENTIETH CENTURIES)

The Sierra Nevada is the highest mountain system on the Iberian Peninsula (Mulhacén 3482 m; Veleta 3308 m) and is located in the extreme SE region of Spain (lat 37°N, long 3°W). Bibliographic resources, particularly from the eighteenth to twentieth centuries, provide insights into the changing summit landscape as the effects of cold, ice, snow and wind shaped its morphology. The selected references emphasize the Sierra's evolving climate reflected in the glaciers and snow hollows, and in the sparse vegetation above certain altitudes. Scientists had established bioclimatic conditions for the entire range in the early nineteenth century, and their works reflect the progression of ideas, particularly in the area of natural sciences, that influenced the period chosen for this study. This information, in addition to current knowledge about the morphogenetic dynamics of the Sierra Nevada, provides the basis for a comparison of the dominant environments from the Little Ice Age to the present, using the most significant high mountain morphological features as a guide. The most relevant findings indicate that cold climate processes (soli‐gelifluction, frost creep and nivation) were more predominant during the eighteenth and nineteenth centuries than they are today.     

Meeting the urban challenge? Urban agriculture and food security in post-conflict Freetown,Sierra Leone

Sierra Leone has recently emerged from a long period of political instability and is ranked among the world's poorest countries. During the decade-long civil war of the 1990s, widespread forced out-migration left much of the countryside abandoned, as rural residents fled to the safety of the capital city, Freetown. Consequently, food production became severely dislocated and, in the post-conflict era, the state of the agricultural sector has become a major concern to governmental and non-governmental development agencies. Focussing on the question of urban food security in Freetown, this paper examines the incidence, dynamics and significance of urban and peri-urban agriculture (UPA) among households, at a crucial point in Sierra Leone's post-conflict reconstruction phase. Drawing on recent field-based data, the paper contributes to the growing debate concerning how urban planning and development might be reconciled with the promotion of an ‘enabling environment’ in which UPA is encouraged and supported. It is argued that in the case of Freetown, a detailed evaluation of UPA is urgently needed to determine how agricultural activities can fit in with urban structure, urban problems and the livelihoods of a wide range of actors in and around the city. The paper concludes that not only is UPA a vital element in ensuring household food security, but it could potentially play a fundamental role in safeguarding the urban food continuum and promoting sustainable urbanization in the post-conflict period and beyond.     

Modelling landfill location using Geographic Information Systems (GIS) and Multi-Criteria Decision Analysis (MCDA): Case study Bo,Southern Sierra Leone

Among the various approaches devised in managing municipal solid wastes, landfills remain the final destination of waste irrespective of the technology used in treating it. Incorrect siting of landfill sites could lead to environmental, social and economic cost; hence, appropriate techniques are required in the identification of potential landfill sites. In densely populated areas in Sierra Leone, there is often tension over the location of landfill sites, where ‘not in my backyard’ campaigns have sparked riots. This article presents a methodological framework for identifying municipal landfill sites in urban areas in Sierra Leone using Bo in Southern Sierra Leone as a case in point. This framework involves a multi-criteria GIS approach that blends two aggregation techniques: Weighted Linear Combination and Ordered Weighted Averaging. Key results show that 83.3% of the study area is unsuitable for municipal landfill.     

Projecting land-use change processes in the Sierra Norte of Oaxaca, Mexico

The objective of study was to explore short-term trends of processes that determine land-use change in Sierra Norte of Oaxaca (SNO), Mexico. Land use and land cover changes (LULCC) were estimated in a complex mosaic of vegetation in the SNO from 1980 to 2000, and projected them to 2020 through a Markovian model. SNO is highly vulnerable to climatic change according to a 2050 GCM scenario. However, 3% annual rate of tropical and temperate forest deforestation from agriculture and livestock encroachment, suggest the threat from land-use change is higher than that from climatic change for this study site. Productive land-use strategies are needed to reduce such high deforestation rates for tropical regions. Controlling deforestation would also reduce short-term effects of CO₂ emissions to the atmosphere. Because of the necessity to evaluate anthropogenic ecosystem changes, it is imperative to separate short-term influences such as deforestation, from long-term influences such as climatic change.     

Decentralization and local institutional arrangements for wetland management in Ethiopia and Sierra Leone

In Ethiopia and Sierra Leone, recent social, political and environmental transformations have precipitated the intensification of wetland use, as local people have sought to safeguard and strengthen their livelihoods. Concurrent decentralization policies in both countries have also seen the government strengthen its position at the local level. Drawing upon recent field-based evidence from Ethiopia and Sierra Leone, this paper examines the compatibility between community-based local institutions for wetland use, and the process of decentralization. It argues that decentralization has in fact restricted the development of mature local institutional arrangements, due to its intrinsically political interventionist nature.     

Fractures and drainage in the granite mountainous area: A study from Sierra Nevada,USA

This paper provides an analysis of relationships between drainage patterns and fractures in the part of Sierra Nevada, California, north of the Yosemite Valley. Bedrock is Cretaceous granite and cut by numerous lineaments of various orientation, length and geomorphic expression. We have mapped fractures and drainage lines from aerial photographs, 1:40 000 scale, in four test areas ranging in size from 32.5 to 266 km². Azimuths are shown on rose diagrams for fractures and drainage lines and then visually and statistically compared. The coincidence of drainage and fracture patterns is strong, which implies causal relationships. In plan, the majority of valleys follow fractures even if this locally means a different orientation in respect to the regional slope arising from tectonic tilt of the range. Main streams occupy deeply incised troughs coincident with ‘master fractures’ of regional extent. Among two principal fracture directions, SSW–NNE to SW–NE and WSW–ENE, the former exerts more control on the drainage lines. The presence of a central zone of structural weakness within the major valleys provided significant constraints for the course of glacial erosion and may explain why multiple Pleistocene glaciers did not succeed in transforming valley cross-sections into expected U-shapes.     

The environmental protection of landscapes in the high semiarid Mediterranean mountain of Sierra Nevada National Park (Spain): Historical evolution and future perspectives

Sierra Nevada is a protected mountain in the Iberian Peninsula classified as a Biosphere Reserve (1986), Natural Park (1989) and National Park (1999). All these environmental protection programmers are a consequence of its unique landscape in the context of the mid-latitude semiarid mountains, with enclaves of exceptional scientific and cultural value. Thanks to its high altitude, Sierra Nevada held the southernmost Quaternary glaciers in Europe, as well as it happened during the Little Ice Age. In turn, Sierra Nevada is also singular thanks to its vast cultural heritage, since very early societies settled on its slopes and valleys and accommodate their lifestyles and economy to the characteristics of this mountain environment. Currently, Sierra Nevada has become an important tourist centre and receives a large amount of visitors. This process of change has conditioned the implementation of a different economic model: it brings benefits to the populations but it involves changes in the landscape as well, sometimes questionable. From this perspective, a critical revision of the legislation is required balancing the sustainable economic development of the population and the preservation and safeguarding of the heritage values of the landscape. With this goal, we suggest creating and implementing the Sites of Geomorphological Interest.     

Spatial Sampling Strategies for Mapping a Volcanic Ground Water Plume in Sierra Valey,California

Accurately mapping a region’s ground water quality depends upon the spatial sampling strategies employed, including where and how often field data are collected. This study compares the relative values of three field sampling strategies for mapping a known migrating plume of volcanic ground water in Sierra Valley, California. The first strategy sampled wells once each year during 1957, 1972, and 1980 (n=63, 45, and 57, respectively) and portrayed spatial–temporal changes in ground water quality more clearly on maps than did two alternative sampling strategies. One of these alternatives, Strategy 2, sampled one well per township per year during 1957, 1972, and 1980 (n=11) and did not detect the migrating plume, despite being a recommended strategy. The other alternative, Strategy 3, frequently sampled in time a small, fixed group of indicator wells (n=13) every four years for the same period, again producing maps with little correlation to the original pattern detected by Strategy 1.     

Spatial Sampling Strategies for Mapping a Volcanic Ground Water Plume in Sierra Valey,California

Accurately mapping a region’s ground water quality depends upon the spatial sampling strategies employed, including where and how often field data are collected. This study compares the relative values of three field sampling strategies for mapping a known migrating plume of volcanic ground water in Sierra Valley, California. The first strategy sampled wells once each year during 1957, 1972, and 1980 (n=63, 45, and 57, respectively) and portrayed spatial–temporal changes in ground water quality more clearly on maps than did two alternative sampling strategies. One of these alternatives, Strategy 2, sampled one well per township per year during 1957, 1972, and 1980 (n=11) and did not detect the migrating plume, despite being a recommended strategy. The other alternative, Strategy 3, frequently sampled in time a small, fixed group of indicator wells (n=13) every four years for the same period, again producing maps with little correlation to the original pattern detected by Strategy 1.     

Chrysophycean cysts in Sierra Nevada (California) lake sediments: paleoecological potential

Thirty-three lakes in the Sierra Nevada range of California were investigated as part of a paleoecological study of the potential effects of acid deposition on sensitive lake/watershed ecosystems. Chrysophyte cysts from surface sediment samples were analyzed and compared with data on pH and alkalinity. This paper identifies the twenty-five dominant chrysophyte cyst taxa and provides information on their morphology, abundance, distribution and ecology.Chrysophycean cysts were generally abundant and well-preserved in lake sediments of our study sites. Twelve taxa occurred in more than twenty of the thirty-three lakes; these taxa were often quite abundant. In contrast, only nine taxa occurred in ten or fewer lakes. Abundance Weighted Mean (AWM) pH varied from 6.45 to 8.34 and AWM alkalinity varied from 46 to 588 eq/L. We delineated pH preference categories, based on AWM pH values and frequency diagrams of cyst abundance vs. lake-water pH. We classified five taxa as acidophilous, nine as circumneutrals, six as alkaliphilous and five as indifferent. Given that the cyst types differ greatly in their abundance relative to pH and alkalinity, it is clear that they have potential for paleolimnological studies of Sierra lakes biogeochemistry.     

Pore Water Pressure as a Trigger of Shallow Landslides in the Western Ghats of Kerala,India: Some Preliminary Observations from an Experimental Catchment

The Western Ghats mountain chain of Kerala, India, is prone to landslides mainly caused by anthropogenic disturbances and very high rainfall amounts. Here, some initial observations on the apparent relationship among pore water pressure fluctuations, rainfall characteristics, and landslide initiation are presented based on monitoring in an experimental catchment in the upper Tikovil River basin. On June 21 and 22, 2007, continuous rain fell for over 10 hours with a total precipitation of 147 mm, causing three shallow landslides in the catchment. Measurements using piezometers in three hollows of the catchment indicate that the rain spell resulted in the development of high pore water pressure from the beginning of the storm that persisted through the time of occurrence of shallow landslides. The pore water pressure patterns in these monitored hollows are possible representatives of the pore water pressure pattern in the hollows where the landslides initiated. This similarity of response pattern enables such data to be used for the calibration and validation of physically based slope hydrology models coupled with slope stability models.     

Hydrophytes of the oases in the Sierra de la Giganta of Central Baja California Sur, Mexico: Floristic composition and conservation status

One of the features of the Sierra de la Giganta mountain range is the existence of many small riparian wetlands (oases) along drainage channels. There are no geohydrological studies from which to determine their dynamics in the arid environment, but these areas confront increasing water extraction to satisfy demands of small local settlements. This study compiled a checklist of the hydrophytes from 12 representative oases, and discusses their current status on the basis of composition, richness, and species characteristics. Floristic composition (absence–presence of 57 hydrophytes) at each location was classified by using UPGMA to represent a dendrogram of group cohesivity. Two major kinds of locations are present. By analysing individual site characteristics, we found that one group occurs in places under “good conservation conditions” and the other composed of locations that are “impacted” in several ways. The former group contains oases that are relatively rich in species, including most of the aquatic forms, which are sensitive to disturbance. Geographical affinity of the floristic list reveals that most species have a broad distribution, mostly in tropical America.     

Diatom-inference models for surface-water temperature and salinity developed from a 57-lake calibration set from the Sierra Nevada, California, USA

Physical, chemical, and biological data were collected from a suite of 57 lakes that span an elevational gradient of 1360 m (2115 to 3475 m a.s.l.) in the eastern Sierra Nevada, California, USA as part of a multiproxy study aimed at developing transfer functions from which to infer past drought events. Multivariate statistical techniques, including canonical correspondence analysis (CCA), were used to determine the main environmental variables influencing diatom distributions in the study lakes. Lakewater depth, surface-water temperature, salinity, total Kjeldahl nitrogen, and total phosphorus were important variables in explaining variance in the diatom distributions. Weighted-averaging (WA) and weighted-averaging partial least squares (WA-PLS) were used to develop diatom-based surface-water temperature and salinity inference models. The two best diatom-inference models for surface-water temperature were developed using simple WA and inverse deshrinking. One model covered a larger surface-water temperature gradient (13.7 °C) and performed slightly poorer (r² = 0.72, RMSE = 1.4 °C, RMSEP_jack = 2.1 °C) than a second model, which covered a smaller gradient (9.5 °C) and performed slightly better (r² = 0.89, RMSE = 0.7 °C, RMSEP_jack = 1.5 °C). The best diatom-inference model for salinity was developed using WA-PLS with three components (r² = 0.96, RMSE = 4.06 mg L^–1, RMSEP_jack = 11.13 mg L^–1). These are presently the only diatom-based inference models for surface-water temperature and salinity developed for the southwestern United States. Application of these models to fossil-diatom assemblages preserved in Sierra Nevada lake sediments offers great potential for reconstructing a high-resolution time-series of Holocene and late Pleistocene climate and drought for California.     

Diatom-inference models for acid neutralizing capacity and nitrate based on 41 calibration lakes in the Sierra Nevada, California, USA

We investigated relationships among modern diatom species composition and physical and chemical characteristics of high-elevation lakes of the Sierra Nevada (California), to develop transfer functions that can be used to infer historic lake conditions. Data were collected from 50 lakes in National Parks and Forests of the central and southern Sierra Nevada. Multivariate statistical methods revealed that acid neutralizing capacity (ANC) and nitrate accounted for significant variation in diatom taxa. A training set with 242 modern diatom taxa from a subset of 41 lakes was used to develop transfer functions for ANC and nitrate using weighted averaging techniques. ANC and nitrate calibration ranges were 23.0–137 μEq/L and 0.18–9.5 μM, respectively. Coefficients of determination for the models were: ANC: R² = 0.76, and R _jackknife ²  = 0.44; NO₃: R² = 0.67, and R _jackknife ²  = 0.27. The ANC model was applied to the top 50 cm of sediments in Moat Lake to reconstruct ANC from ca. AD 350 to 2005. The reconstruction suggests that ANC declined by about 40 % (101–60 μEq/L) between the 1920s and the 1960s and then recovered to pre-1920s levels during 1980–2000. The magnitude of this ANC excursion was the largest observed during the past 1,600 years. We hypothesize that temporal variations in ANC were influenced by: (1) changes in rates of acid deposition, especially nitric acid and (2) variations in the timing and magnitude of snowmelt runoff.     

RADIOCARBON DATING OF GLACIAL MORAINES USING THE AEOLIAN BIOME: TEST RESULTS AT BISHOP CREEK,SIERRA NEVADA,CALIFORNIA

Radiocarbon measurements on fossilized remnants of the aeolian biome, incorporated in glacial moraines in the Sierra Nevada of California, are consistent with the relative order of moraines at Bishop Creek, on the eastern slopes of the Sierra Nevada. Holocene ¹⁴C ages correspond with periods of more effective moisture according to paleoecological and treeline data in the range, whereas Pleistocene ages are penecontemporaneous with Heinrich Events in the North Atlantic. These findings must be interpreted with caution, however, owing to a number of uncertainties, including: evidence that younger contaminants are added to till matrix; the possibility of older contaminants; the effects of pretreatment on aeolian biome remains; and processes by which organics undergo diagenesis within till matrices in different biogeochemical settings. [Key words: aeolian biome, Heinrich Events, moraines, radiocarbon dating, Sierra Nevada.]