Collaborative research: Testing hypothesis for drumlin fomation at Mulajokul, Iceland

合作研究：检验冰岛穆拉霍库鼓林构造的假设

• 批准号: 1540156
• 负责人: Neal Iverson
• 金额: $ 3.55万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-03-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1540156&HistoricalAwards=false
• 关键词: Collaborative; research; Testing; hypothesis; drumlin

The leading hypothesis for the formation of drumlins--elongate hills that form beneath sediment-floored glaciers--is that they are nucleated where low pore-water pressure in the sediment bed inhibits its shear. These parts of the bed may resist erosion and prompt local deposition, causing hills to form. However, a drumlin field recently exposed by the retreat of the surge-type Icelandic glacier, Múlajökull, provides a compelling alternative hypothesis: that drumlins form in zones of low effective stress (total ice pressure minus pore-water pressure) associated with swarms of longitudinal crevasses in the glacier margin. These two hypotheses lead to predictions of effective-stress and bed-deformation patterns that are conspicuously different. During two field seasons, these patterns will be studied at Múlajökull by trenching drumlins and their intervening swales and then collecting intact till specimens for two kinds of analyses. Some samples will be compacted in consolidation tests, a well-established technique for inferring the past maximum effective stress on former glacier beds that has not yet been applied systematically to drumlins. Other samples will have their anisotropy of magnetic susceptibility (AMS) measured, and preferred orientations of susceptibility will be used to determine patterns of deformation in the drumlins and intervening areas. If past effective stresses were anomalously low in drumlins, the leading hypothesis for their formation would be contradicted, and the crevasse hypothesis would be supported. The same would be true if AMS patterns were either not related to drumlin morphology or indicated convergent shear of bed sediments toward the up-glacier ends of drumlins. The origin of drumlins, which cover vast areas of Canada, Scandinavia, Britain, Ireland, and the northern U.S., is one of the longest standing problems in Earth science. Although drumlins have been the subject of over 1300 scientific contributions since their study began ~150 years ago, the origin of no drumlin field is known definitively. By focusing on a drumlin field that is "active" in the sense that it has been shaped by the current glacial regime and studying drumlin sediments in new ways, this research in central Iceland will help illuminate the processes that sculpt one of the most emblematic and mysterious of glacial landforms. Results will also provide guidance for predicting the distribution of drag at the beds of ice sheets, a fundamental factor in estimating their speeds. This project will support the education of two graduate students and will provide international independent study projects for six undergraduate students from underrepresented groups. A request will be made for a high school teacher, supported by the NSF-supported PolarTREC program, to participate in the field work. This teacher would stream his or her experiences daily back to multiple classrooms with the goals of exposing K-12 students to glacial geologic research and interactively answering their questions.This project is co-supported by the Geomorphology and Land Use Dynamics program and the Office of International Science and Engineering.

鼓林（在沉积物冰川下方形成的细长山丘）形成的主要假设是，它们在沉积物床中的低孔隙水压力抑制其剪切力的地方形成核，这些部分可以抵抗侵蚀并促进沉积物的形成。然而，最近由于汹涌型冰岛冰川穆拉冰川的退缩而暴露出的鼓林区，提供了一个令人信服的替代假设：鼓林是在低洼地区形成的。有效应力（总冰压力减去孔隙水压力）与冰川边缘的大量纵向裂缝有关，这两种假设导致对有效应力和河床变形模式的预测在两个野外季节中明显不同。将在穆拉冰川进行研究，方法是挖掘鼓林及其中间的洼地，然后收集完整的耕作样本进行两种分析，一些样本将在固结测试中进行压实。用于推断前冰川床上过去最大有效应力的成熟技术尚未系统地应用于鼓林，将测量其他样本的磁化率各向异性（AMS），并将使用磁化率的首选方向来确定模式。如果鼓林和干预区域过去的有效应力异常低，则其形成的主要假设将被矛盾，裂缝假设将成立。如果 AMS 模式与鼓林形态无关或表明河床沉积物向鼓林冰川末端汇聚剪切，则同样如此。和美国北部，是地球科学中最长期存在的问题之一，尽管自大约 150 年前开始研究以来，鼓林已经成为 1300 多项科学贡献的主题，但没有任何起源。通过关注由当前冰川状态塑造的“活跃”的鼓林场，并以新的方式研究鼓林沉积物，这项在冰岛中部进行的研究将有助于阐明塑造鼓林场的过程。最具象征意义和神秘的冰川地貌之一，其结果还将为预测冰盖床阻力的分布提供指导，这是估计冰盖速度的基本因素，该项目将支持两名研究生的教育，并将提供帮助。为来自代表性不足群体的六名本科生开展国际独立研究项目，将请求一名高中教师在 NSF 支持的 PolarTREC 项目的支持下参与实地工作。多个教室，目的是让 K-12 学生接触冰川地质研究并交互式回答他们的问题。该项目由地貌学和土地利用动力学项目以及国际科学与工程办公室共同支持。