Collaborative research: Testing hypotheses for drumlin formation at Mulajokull, Iceland

鼓石--在被沉积物覆盖的冰川下形成的细长山丘--形成的主要假说是，它们是在沉积物床中的低孔压抑制其剪切时成核的。河床的这些部分可能会抵抗侵蚀，促使局部沉积，导致丘陵的形成。然而，最近冰岛涌浪型冰川MúLajökull的退缩暴露出的鼓状物提供了一个令人信服的替代假设：鼓状物形成于与冰川边缘大量纵向裂缝相关的低效应力区(总冰压减去孔隙水压力)。这两个假设导致了对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，方法是挖出鼓声和它们之间的沟槽，然后完整地收集TIL标本进行两种分析。一些样品将在固结试验中压实，这是一种成熟的技术，用于推断以前冰川床上过去的最大有效应力，但尚未系统地应用于鼓形物。其他样品的磁化率各向异性(AMS)将被测量，磁化率的优先取向将被用来确定鼓形和中间区域的变形模式。如果过去的有效应力在鼓声中异常低，则形成鼓声的主要假说将是矛盾的，而裂缝假说将得到支持。如果AMS模式要么与鼓状形态无关，要么表明河床沉积物向鼓状冰川上游的汇聚剪切，情况也是如此。鼓声的起源覆盖了加拿大、斯堪的纳维亚半岛、英国、爱尔兰和美国北部的广大地区，是地球科学中历史最悠久的问题之一。虽然鼓声自150年前开始研究以来，已经有1300多篇科学贡献，但没有鼓声的起源是确定的。冰岛中部的这项研究将重点放在一个被当前冰川制度塑造的鼓状区域，并以新的方式研究鼓状沉积物，这将有助于阐明塑造这一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面上的阻力分布提供指导，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。将请求一名高中教师在国家科学基金会支持的PolarTREC计划的支持下参与实地工作。这位教师每天将他或她的经验流传回多个教室，目标是让K-12学生接触冰川地质研究并互动回答他们的问题。该项目由地貌学和土地利用动力学项目和国际科学与工程办公室共同支持。

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.