Lavakas: investigating extreme erosion in Madagascar

拉瓦卡斯：调查马达加斯加的极端侵蚀

• 批准号: 0415439
• 负责人: Rónadh Cox
• 金额: $ 22.52万
• 依托单位: Williams College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-15 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0415439&HistoricalAwards=false
• 关键词: Lavakas; investigating; extreme; erosion; Madagascar

Extreme erosion characterizes Madagascar's central highlands. The country has a "world-record erosion rate" according to the World Bank, and the widespread hillslope gullies called lavaka are featured in every guidebook as examples of the catastrophic denudation of the country.s landscape. Lavakas, which have been described as .cat claw-marks. on the landscape, initiate suddenly and grow rapidly, shedding sediment volumes on the order of 8000 m3 in a few months. They cause substantial infrastructural problems because they undermine roads and bridges, and because the debris flows that issue from them swamp agricultural land. They are widely cited as being largely or entirely anthropogenic in origin, and the major source of high sediment loads in Madagascar's rivers. Neither of these interpretations is based on hard data, however, and in spite of the importance of this issue, both from an economic and an environmental point of view, of erosion are largely unstudied. Strong statements abound, but there are no data to constrain the rates at which lavakas form, or their relative contribution to regional sediment budgets; and the geological controls on their formation are largely unknown. The proposed project will address the issue of modern erosion in Madagascar by investigating rates of lavaka formation and geological controls on their initiation. Analysis of changes in lavaka distribution and size will be achieved by combining air photo mapping of lavaka distributions 60 years ago and field mapping of present-day lavaka distributions in a GIS database. This will permit evaluation of decadal-scale sediment generation volumes, as well as lavaka evolution rates. Cosmogenic isotope analysis will produce sediment generation rates on the millennial scale, which can be compared with the mapping-derived rates of recent erosion to evaluate whether erosion rates have in fact increased in recent time as has been frequently asserted but never demonstrated. Quantification of human effects on lavaka formation and growth will be achieved by GIS analysis of mapped distributions of lavakas and their relationship to different land-use categories. Understanding of geologic controls on the location of lavakas will come from detailed mapping of the structural geology of underlying saprolitized bedrock and slope characteristics. The results of this project will be of significance to studies of human interactions with the landscape in general. They will have direct relevance for environmental planning and erosion mitigation strategies for Madagascar. Establishment of geologic criteria predisposing some slopes to lavaka formation could save enormous amounts of money by providing preventive planning strategies for road and dam building organizations. Above all, understanding the role of lavakas in sediment generation; the role of humans in lavaka formation; and whether Madagascar is naturally characterized by high erosion rates or whether they are of recent and anthropogenic origin, will solidify thinking about ecological strategizing in Madagascar and contribute to a better understanding of the islands exogenic system as a whole. This project will be a wonderful way to train students in the process of approaching a scientific problem that has direct societal relevance. Linking education and international collaboration is also a key component of this project. Undergraduate students, both American and Malagasy, will get intense one-on-one mentoring and training in the field and in the lab, as well as hands-on experience with a variety of analytical tools and GIS/remote sensing techniques. The project will provide opportunities for third-world Malagasy students to travel to the U.S. for education and training, and will also create career training and research opportunities for Malagasy collaborators.This award is co-funded by the Division of Earth Science and the Office of International Science and Education.

严重的侵蚀是马达加斯加中部高地的特征。 根据世界银行的说法，该国拥有“世界纪录的侵蚀率”，而被称为lavaka的广泛山坡沟壑在每一本旅游指南中都作为该国景观灾难性剥蚀的例子。 拉瓦卡，被描述为猫爪印。在景观上，突然开始并迅速增长，在几个月内脱落的沉积物量约为8000立方米。 它们造成严重的基础设施问题，因为它们破坏道路和桥梁，而且因为它们产生的泥石流淹没了农田。 它们被广泛认为主要或完全是人为的，是马达加斯加河流中高沉积物的主要来源。 这两种解释都不是基于确凿的数据，然而，尽管从经济和环境的角度来看，这一问题很重要，但侵蚀在很大程度上没有得到研究。 强有力的声明比比皆是，但没有数据来限制熔岩形成的速度，或者它们对区域沉积物预算的相对贡献;它们形成的地质控制在很大程度上是未知的。拟议的项目将通过调查lavaka形成的速度及其开始的地质控制来解决马达加斯加的现代侵蚀问题。将通过将60年前拉瓦卡分布的航空照片制图与GIS数据库中当今拉瓦卡分布的实地制图相结合，来分析拉瓦卡分布和大小的变化。 这将有助于评估十年尺度的沉积物生成量以及拉瓦卡演变率。 宇宙成因同位素分析将得出千年尺度的沉积物生成率，可将其与测绘得出的近期侵蚀率进行比较，以评估侵蚀率是否如经常断言但从未得到证实的那样在近期实际上有所增加。 将通过地理信息系统分析绘制的拉瓦卡分布图及其与不同土地使用类别的关系，量化人类对拉瓦卡形成和生长的影响。 对拉瓦卡斯位置的地质控制的理解将来自对下面的腐泥土化基岩和斜坡特征的结构地质的详细测绘。 该项目的结果将对人类与景观相互作用的研究具有重要意义。 它们将直接关系到马达加斯加的环境规划和减少侵蚀战略。 通过为道路和水坝建设组织提供预防性规划策略，建立地质标准可以使一些斜坡倾向于形成拉瓦卡层，从而节省大量资金。 最重要的是，了解lavakas在沉积物生成中的作用;人类在lavaka形成中的作用;以及马达加斯加是否自然地以高侵蚀率为特征，或者它们是否是最近和人为的起源，将巩固对马达加斯加生态战略的思考，并有助于更好地了解整个岛屿的外源系统。这个项目将是一个很好的方式来培养学生在接近一个科学问题的过程中，有直接的社会相关性。 将教育与国际合作联系起来也是该项目的一个关键组成部分。 本科生，无论是美国人还是马达加斯加人，都将在现场和实验室中获得一对一的指导和培训，以及各种分析工具和GIS/遥感技术的实践经验。 该项目将为来自第三世界的马达加斯加学生提供前往美国接受教育和培训的机会，并为马达加斯加合作者创造职业培训和研究机会。该奖项由地球科学部和国际科学与教育办公室共同资助。