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.

关于鼓丘（在沉积物覆盖的冰川下形成的细长山丘）形成的主要假设是，它们是在沉积物床的低孔隙水压力抑制其剪切的地方成核的。河床的这些部分可以抵抗侵蚀并促使局部沉积，从而形成山丘。然而，最近由于冰岛激流型冰川（Múlajökull）的退缩而暴露出的一个鼓点区提供了一个令人信服的替代假设：鼓点形成于与冰川边缘纵向裂缝群相关的低有效应力区（总冰压减去孔隙水压力）。这两种假设导致有效应力和床层变形模式的预测明显不同。在两个野外季节，这些模式将在Múlajökull进行研究，方法是挖掘鼓丘及其中间的沟槽，然后收集完整的till标本进行两种分析。一些样品将在固结试验中被压实，这是一种成熟的技术，用于推断过去在前冰川床上的最大有效应力，但尚未系统地应用于鼓体。其他样品将测量其磁化率的各向异性（AMS），磁化率的首选方向将用于确定鼓体和中间区域的变形模式。如果鼓点过去的有效应力异常低，则其形成的主要假设将被推翻，而裂缝假设将得到支持。如果AMS模式要么与鼓鼓形态无关，要么表明河床沉积物向鼓鼓的冰川上端收敛剪切，情况也是如此。鼓槌分布在加拿大、斯堪的纳维亚半岛、英国、爱尔兰和美国北部的广大地区，其起源是地球科学中长期存在的问题之一。尽管自150年前开始研究鼓鼓以来，已有1300多项科学贡献，但没有一个鼓鼓场的起源是明确的。通过关注一个“活跃”的鼓林场，它已经被当前的冰川制度所塑造，并以新的方式研究鼓林沉积物，这项在冰岛中部的研究将有助于阐明塑造最具象征意义和最神秘的冰川地貌之一的过程。结果还将为预测冰盖床上的阻力分布提供指导，这是估计冰盖速度的一个基本因素。该项目将支持两名研究生的教育，并将为来自代表性不足群体的六名本科生提供国际独立学习项目。申请一名高中教师，由美国国家科学基金会支持的PolarTREC项目支持，参加实地工作。这位老师每天都会将他或她的经验反馈给多个教室，目的是让K-12学生了解冰川地质研究，并互动地回答他们的问题。该项目由地貌与土地利用动力学项目和国际科学与工程办公室共同支持。