Erosion rates in the southern oregon coast range: Evidence for an equilibrium between hillslope erosion and sediment yield

The relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm³cm^?1yr^?1 and average bedrock lowering rates of about 0.07 mm yr^?1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr^?1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin-wide denudation rates of between 0.05 and 0.08mm yr^?1, suggesting an approximate steady-state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km², suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape.     

The effects of rock uplift and rock resistance on river morphology in a subduction zone forearc,Oregon, USA

Relationships between riverbed morphology, concavity, rock type and rock uplift rate are examined to independently unravel the contribution of along-strike variations in lithology and rates of vertical deformation to the topographic relief of the Oregon coastal mountains. Lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology. Volcanic and sedimentary rocks are the principal rock types underlying the northern Oregon Coast Ranges (between 46°30′ and 45°N) where mixed bedrock–alluvial channels dominate. Average concavity, θ, is 0·57 in this region. In the alluviated central Oregon Coast Ranges (between 45° and 44°N) values of concavity are, on average, the highest (θ = 0·82). South of 44°N, however, bedrock channels are common and θ = 0·73. Mixed bedrock–alluvial channels characterize rivers in the Klamath Mountains (from 43°N south; θ = 0·64). Rock uplift rates of ≥0·5 mm a⁻¹, mixed bedrock–alluvial channels, and concavities of 0·53–0·70 occur within the northernmost Coast Ranges and Klamath Mountains. For rivers flowing over volcanic rocks θ = 0·53, and θ = 0·72 for reaches crossing sedimentary rocks. Whereas channel type and concavity generally co-vary with lithology along much of the range, rivers between 44·5° and 43°N do not follow these trends. Concavities are generally greater than 0·70, alluvial channels are common, and river profiles lack knickpoints between 44·5° and 44°N, despite the fact that lithology is arguably invariant. Moreover, rock uplift rates in this region vary from low, ≤0·5 mm a⁻¹, to subsidence (<0 mm a⁻¹). These observations are consistent with models of transient river response to a decrease in uplift rate. Conversely, the rivers between 44° and 43°N have similar concavities and flow on the same mapped bedrock unit as the central region, but have bedrock channels and irregular longitudinal profiles, suggesting the river profiles reflect a transient response to an increase in uplift rate. If changes in rock uplift rate explain the differences in river profile form and morphology, it is unlikely that rock uplift and erosion are in steady state in the Oregon coastal mountains. Copyright © 2006 John Wiley & Sons, Ltd.     

Excess in precipitation as a cause for settlement decline along the Israeli coastal plain during the third millennium BC

Although the relations between climate and settlement are not straightforward, there is a general agreement that arid conditions are less favorable for human settlement in the semiarid Near East than humid conditions. Here we show that humid conditions resulted in the abandonment of settlements along the Israeli coastal plain. We first present archaeological evidence for a drastic decline in settlement along the Israeli coast during most of the third millennium BC (Early Bronze Age II-III). Then, based on archaeological and climatic evidence, we link this decline to an environmental change occurring at that time. We propose that increased precipitation intensified the already existing drainage problems and resulted in flooding, which led to the transformation of arable land into marshes and to the spread of diseases, gradually causing settlement decline and abandonment.     

山东省蓬莱市蝎子顶金矿地质特征

蓬莱市蝎子顶金矿容矿构造为NW向断裂,具NW向成串分布的特点。NW向压扭性断裂与其派生的断裂裂隙系统是该区金矿床赋存空间的重要构造标志,构造破碎带中的钾化、硅化、黄铁绢英岩化等蚀变是一种直接找矿标志。通过对矿床地质特征的研究,认为该矿床属岩浆低中温热液充填交代蚀变岩型金矿床。     

渤海海峡亚海鲂属鱼类一新记录种——云纹亚海鲂

2012年12月3日,在渤海海峡的蓬莱近海浅水海域捕获雄性成体鱼1尾,该鱼体长34 cm,体高18cm,体长为体高的1.9倍,体宽4.5 cm,头长12.5 cm,体长为头长的2.7倍,尾柄长4.5 cm,体光滑无鳞。管状侧线前半部弧形,后半部平直,行于体中央。棘状骨板沿背鳍基底两侧各12块,臀鳍基底两侧各8块,每一骨板中央具1棘,向后;胸部6块,自第3骨板开始分左右两行;腹部7块,自第2骨板开始分左右两行,胸腹部骨板棘小,形成锯齿缘。背鳍1个,鳍棘部与鳍条部之间有一深缺刻;鳍棘细长,棘间鳍膜延长成丝状,最长超过尾鳍末端。据其形态特征和测量值,鉴定为云纹亚海鲂(Zenopsis nebulosa Temminck et Schlegel,1847),为该海域首次记录。     

“工程测量”实践教学体系的研究与构建

工程测量是港口航道与海岸工程专业技术人员必须掌握的基本技能之一。为解决应用型本科院校工程测量课程的实践教学体系与应用型人才培养目标要求不相适应的问题,从剖析实践教学过程中存在的现实问题出发,结合学校及专业实际情况,以大连海洋大学港口航道与海岸工程专业为例,提出了一套完整的、操作性强、专业特色鲜明的实践教学体系,并取得了一定的教学成果,对于普通高等学校应用型人才的培养具有重要的借鉴意义。     

The influence of upper-crust lithology on topographic development in the central Coast Ranges of California

A fundamental geological tenet is that as landscapes evolve over graded to geologic time, geologic structures control patterns of topographic distribution in mountainous areas such that terrain underlain by competent rock will be higher than terrain underlain by incompetent rock. This paper shows that in active orogens where markedly weak and markedly strong rocks are juxtaposed along contacts that parallel regional structures, relatively high topography can form where strain is localized in the weak rock. Such a relationship is illustrated by the topography of the central Coast Ranges between the Pacific coastline and the San Andreas fault zone (SAFZ), and along the length of the Gabilan Mesa (the “Gabilan Mesa segment” of the central Coast Ranges). Within the Gabilan Mesa segment, the granitic upper crust of the Salinian terrane is in contact with the accretionary-prism mélange upper crust of the Nacimiento terrane along the inactive Nacimiento fault zone. A prominent topographic lineament is present along most of this lithologic boundary, approximately 50 to 65 km southwest of the SAFZ, with the higher topography formed in the mélange on the southwest side of the Nacimiento fault.This paper investigates factors influencing the pattern of topographic development in the Gabilan Mesa segment of the central Coast Ranges by correlating shortening magnitude with the upper-crust compositions of the Salinian and Nacimiento terranes. The fluvial geomorphology of two valleys in the Gabilan Mesa, which is within the Salinian terrane, and alluvial geochronology based on optically-stimulated luminescence (OSL) age estimates, reveal that the magnitude of shortening accommodated by down-to-the-southwest tilting of the mesa since 400 ka is less than 1 to 2 m. Our results, combined with those of previous studies, indicate that at least 63% to 78% of late-Cenozoic, northeast-southwest directed, upper-crustal shortening across the Gabilan Mesa segment has been accommodated within the Nacimiento terrane. This is significant because perpendicular to orogenic strike the Nacimiento terrane constitutes less than ¼ of the distance between the coast and the SAFZ, and the other ¾ (or greater) of the distance between the coast and the SAFZ is underlain by the granitic upper crust of the Salinian terrane. We propose that strain and mountain building are localized within the Nacimiento terrane because it consists predominantly of the relatively weak Franciscan Complex mélange, and because the upper crust of the Salinian terrane is composed of relatively strong granitic rocks. Our hypothesis is supported by the distribution of post-seismic surface uplift associated with the 2003, 6.5 M_W San Simeon earthquake, which mimics the topography of the southwestern part of the Gabilan Mesa segment of the central Coast Ranges.     

Evolution of east coast of India — A plate tectonic reconstruction

The evolution of east coast of India sis discussed within the ambit of clearly identifiable four major tectonic stages which had a profound effect in shaping the tectonic grain of the east coast basins. The evolutionary process began with rift related crustal extension between India and Sri Lanka as a consequence of Africa-Antarctica rifting and development of Natal Basin. An arm of this rift led to initial extension in the Cauvery Basin and failed. Later, the India-West Australia rift propagated further in southwesterly direction initiating Mahanadi and Krishna-Godavari Basins. This extension was an oblique one with Nayudupeta high acting as pivot. The oblique extension followed by asymmetric seafloor spreading developed transpression along India-Sri Lanka and Antarctica junction, resulting in a NNW-SSE trending transcurrent fault along which Antarctica moved southward. Subsequently, entire east coast evolved through a more or less uniform post rift stage.     

Quantifying sedimentation patterns of small landslide-dammed lakes in the central Oregon Coast Range

Understanding sedimentation patterns in small coastal watersheds due to landscape perturbations is critical for connecting hillslope and fluvial processes, in addition to managing aquatic habitats for anadromous fish and other aquatic species in the Oregon Coast Range (OCR). Changes in sedimentation patterns spanning the last 250 years are preserved in two landslide-dammed lakes in small watersheds (< 10 km²) underlain by the Tyee Formation in the central OCR. Dendrochronology of drowned Douglas-fir stumps in both lakes provided precise timing of the damming and formation of the lakes, with Klickitat Lake forming in winter ad 1751/52 and Wasson Lake in winter ad 1819/20. Perturbations from wildfires, logging and road development, and previously underappreciated snow events affect sedimentation rates in the lakes to different degrees, and are identified in the sediment record using cesium-137 (¹³⁷Cs), high-resolution charcoal stratigraphy, local fire records, and aerial photography. Each lake has variable sedimentation accumulation rates (0.05–4.4 cm yr⁻¹) and mass accumulation rates (0.02–1.42 g cm⁻² yr⁻¹). Sedimentation rates remained low from the landslide-damming events until the mid-19th century, when they increased following stand-replacing wildfires. Aside from a sediment remobilization triggered by human modification of the landslide dam at Klickitat Lake around 1960, the largest peaks in mass accumulation rates in the mid-20th century at both lakes in the early 1950s precede major road construction and logging activity in the watersheds. Subsequent sedimentation rates are lower, but variable, and possible effects of logging and road development might be exacerbated by abnormal precipitation and heavy snow events. A comparison of previous studies of landslide-dammed lakes in larger watershed of the OCR are consistent with our findings of increased sedimentation in the mid-20th century, as well as higher sedimentation rates in the debris-flow dominated southern Tyee Formation than in the lower-relief northern Tyee Formation.