Mangrove forests: Resilience,protection from tsunamis,and responses to global climate change

This review assesses the degree of resilience of mangrove forests to large, infrequent disturbance (tsunamis) and their role in coastal protection, and to chronic disturbance events (climate change) and the future of mangroves in the face of global change. From a geological perspective, mangroves come and go at considerable speed with the current distribution of forests a legacy of the Holocene, having undergone almost chronic disturbance as a result of fluctuations in sea-level. Mangroves have demonstrated considerable resilience over timescales commensurate with shoreline evolution. This notion is supported by evidence that soil accretion rates in mangrove forests are currently keeping pace with mean sea-level rise. Further support for their resilience comes from patterns of recovery from natural disturbances (storms, hurricanes) which coupled with key life history traits, suggest pioneer-phase characteristics. Stand composition and forest structure are the result of a complex interplay of physiological tolerances and competitive interactions leading to a mosaic of interrupted or arrested succession sequences, in response to physical/chemical gradients and landform changes. The extent to which some or all of these factors come into play depends on the frequency, intensity, size, and duration of the disturbance. Mangroves may in certain circumstances offer limited protection from tsunamis; some models using realistic forest variables suggest significant reduction in tsunami wave flow pressure for forests at least 100 m in width. The magnitude of energy absorption strongly depends on tree density, stem and root diameter, shore slope, bathymetry, spectral characteristics of incident waves, and tidal stage upon entering the forest. The ultimate disturbance, climate change, may lead to a maximum global loss of 10–15% of mangrove forest, but must be considered of secondary importance compared with current average annual rates of 1–2% deforestation. A large reservoir of below-ground nutrients, rapid rates of nutrient flux and microbial decomposition, complex and highly efficient biotic controls, self-design and redundancy of keystone species, and numerous feedbacks, all contribute to mangrove resilience to various types of disturbance.     

Effect of the Bottom Topography on Tsunami Propagation in the East （Japan） Sea

A study of tsunami events in the East （Japan） Sea using continuous Galerkin finite element model, aiming at reproducing tsunami waves generated by underwater earthquakes in 1983 and 1993 respectively has been performed focusing on the geographic extent of a topographic feature in the East （Japan） Sea. Numerical models can be the proper tools to study the combined effects of realistic topography. Subsequently, using the FEM based two-dimensional model we have simulated the smoothed and flattened topographic effects by removal of Yamato Rise and seamounts for the cases of tthe 1983 Central region earthquake tsunami and the 1993 southwestern Hokkaido earthquake tsunami. The results have shown that there will be higher tsunamis along the eastern coasts of Korea in general except some areas, like Sokcho with removal of topographic highs, thus providing complicated bottom topography of the East （Japan） Sea as effective tsunami energy scattering.     

Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland,Scotland

We reconstruct one of the longest relative sea‐level (RSL) records in north‐west Europe from the north coast of mainland Scotland, using data collected from three sites in Loch Eriboll (Sutherland) that we combine with other studies from the region. Following deglaciation, RSL fell from a Lateglacial highstand of +6?8 m OD (Ordnance Datum = ca. mean sea level) at ca. 15 k cal a BP to below present, then rose to an early Holocene highstand and remained at ca. +1 m OD between ca. 7 and 3 k cal a BP, before falling to present. We find no evidence for significant differential Holocene glacio‐isostatic adjustment between sites on the north‐west (Lochinver, Loch Laxford), north (Loch Eriboll) and north‐east (Wick) coast of mainland Scotland. This suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region. From one site at the head of Loch Eriboll we report the most westerly sedimentary evidence for the early Holocene Storegga tsunami on the Scottish mainland. The presence of the Storegga tsunami in Loch Eriboll is predicted by a tsunami wave model, which suggests that the tsunami impacted the entire north coast of Scotland and probably also the Atlantic coastline of north‐west Scotland.

     

黄河三峡库区滑坡诱发的涌浪预测方法

黄河三峡库区的涌浪灾害风险不容忽视,经验公式是宜优先考虑的涌浪快捷评价方法.对黄河三峡焦家崖头2012年2月7日的黄土滑坡和涌浪进行调查,分析了黄土滑坡及涌浪的特征.采用9种涌浪经典计算公式,计算了涌浪的初始浪高、对岸爬高等特征参数.与调查结果对比表明,采用美国土木工程师协会推荐法、水科院算法、Huber and Hager模型和潘家铮算法获取的焦家崖头黄土滑坡诱发的涌浪特征参数均接近实际,其确定的校正系数分别为2.14、1.92、0.6和0.66,对比考虑安全性和经济性后推荐采用潘家铮算法预测黄河三峡的涌浪.     

葡萄牙破坏性地震和海啸预警系统(DETWS)

本文介绍了葡萄牙破坏性地震和海啸预警系统(Destructive Earthquakes and Tsunami Warning System)的构成、地震与海啸信息的检测、海啸预警信息的发布。     

2004年12月26日苏门答腊-安达曼大地震构造特征及地震海啸灾害

2004年12月26日在印度尼西亚苏门答腊岛西侧海域发生的地震是自1964 年阿拉斯加大地震以来最大的地震,震级达到9级或9级以上。它是由印度洋板块向缅甸微板块底下俯冲过程中的逆断层作用造成的。印度洋板块以每年6~7 cm的速率向北北东方向运动,与南亚板块发生斜向聚敛俯冲,此运动在该地区解耦为印度洋板块沿巽他海沟的正向俯冲及缅甸微板块东侧的右旋走向平移运动。主震破裂模型研究的结果表明,破裂是由南向北传播的,地震破裂带长达1 200余km,宽度约100 km,最大位移约为20 m,地震断层向上穿透海沟底面,估计约有10 m左右的错距。这次大地震的同震效应导致地球自转轴摆动、地球自转加速,日长缩短。据目前统计,地震引发的大海啸造成305 276人死亡,被此次海啸夺走生命的人数超过了有史以来历次大海啸灾难中死亡人数的总和。     

Carbonates within a Pleistocene glaciomarine succession, Yakataga Formation, Middleton Island, Alaska

Uplifted during the 1964 Alaskan earthquake, extensive intertidal flats around Middleton Island expose 1300 m of late Cenozoic (Early Pleistocene) Yakataga Formation glaciomarine sediments. These outcrops provide a unique window into outer shelf and upper slope strata that are otherwise buried within the south‐east Alaska continental shelf prism. The rocks consist of five principal facies in descending order of thickness: (i) extensive pebbly mudstone diamictite containing sparse marine fossils; (ii) proglacial submarine channel conglomerates; (iii) burrowed mudstones with discrete dropstone layers; (iv) boulder pavements whose upper surfaces are truncated, faceted and striated by ice; and (v) carbonates rich in molluscs, bryozoans and brachiopods. The carbonates are decimetre scale in thickness, typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope. Biogenic components originated in a moderately shallow (ca 80 m), relatively sediment‐free, mesotrophic, sub‐photic setting. These components are a mixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand‐size bryozoan and echinoderm fragments. Ice‐rafted debris is present throughout these cold‐water carbonates that are thought to have formed during glacial periods of lowered sea‐level that allowed coastal ice margins to advance near to the shelf edge. Such carbonates were then stranded during subsequent sea‐level rise. Productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal‐current winnowing near the ice front. Redeposition was the result of intense storms and possibly tsunamis. These sub‐arctic mixed siliciclastic‐carbonate sediments are an end‐member of the Phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late Palaeozoic southern hemisphere deglaciation.     

Tsunami sediments and their foraminiferal assemblages

Tsunami hazard assessment begins with a compilation of past events that have affected a specific location. Given the inherent limitations of historical archives, the geological record has the potential to provide an independent dataset useful for establishing a richer, chronologically deeper time series of past events. Recent geological studies of tsunami are helping to improve our understanding of the nature and character of tsunami sediments. Wherever possible, geologists should be working to improve the research ‘tool kit’ available to identify past tsunami events. Marine foraminifera (single celled heterotrophic protists) have often been reported as present within tsunami-deposited sediments but in reality, little information about environmental conditions, and by analogy, the tsunami that deposited them, has been reported even though foraminifera have an enormous capacity to provide meaningful palaeo-environmental data. Here, we review what foraminifera are, describe their basic form and significance, summarise where they have been reported in tsunami sediments and identify what can be learnt from them. We review the gaps in our understanding and make recommendations to assist researchers who examine foraminiferal assemblages in order to enhance their use within tsunami geology.     

Post‐tropical/post‐tsunami: Climate and architectural discourse in South and Southeast Asia

Following the Indian Ocean tsunami on 26 December 2004, scenes of destruction overwrote representations of a benign tropical landscape on the eastern periphery of the Indian Ocean. The incongruous coupling of luxury resort hotels with devastated indigent fisher settlements in international media coverage had exposed the global inequities embedded in a tropical tourism industry subscribed to and abetted by states, institutions, developers and architects. As post‐tsunami reconstruction commenced, it became evident that the climatic trope through which regionalist aesthetics had been filtered thus far was incapable of providing expedient solutions to real social problems. In academia and in the profession, the complex discourse of so‐called tropical architecture shaping the debates has yet to be untangled and problematized. Implicating and haunted by colonial, nationalist, developmental and political renderings, and more recently by issues of globalization, such representations continue to undergird architectural debates and production. In the wake of recent reconstruction projects and provoked by related architectural student designs in Sri Lanka, this paper reviews the politics of the tropical agenda in architecture and some considerations for its demise.     

First indication of Storegga tsunami deposits from East Greenland

A 2.73 m long sediment sequence from Loon Lake, located at 18 m a.s.l. on outer Geographical Society Ø, East Greenland, was investigated for its chronology and changes in physical and biogeochemical properties, macrofossils, and grain‐size distribution. The predominance of marine fossils throughout the sequence, dated by ¹⁴C AMS to between 8630 and 7535 cal. yr BP, shows that the Loon Lake at that time was a marine basin, which according to existing sea‐level curves was about 15–35 m deep. The sequence mainly consists of fine grained homogeneous sediments, which are interrupted by a 0.72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain‐size distribution and in the physical and biogeochemical properties. According to the radiocarbon dates, this sandy horizon was deposited after 8500–8300 cal. yr BP and is interpreted as originating from the Storegga tsunami. The record from Loon Lake provides the first indication of Storegga tsunami deposits from East Greenland. Copyright © 2006 John Wiley & Sons, Ltd.