Characteristics of lateral-frontal moraine formed at Arctic and Alpine glaciers
Characteristics of lateral-frontal moraine formed at Arctic and Alpine glaciers
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北极和高山冰川形成的侧额冰碛的特征
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发表时间：
2016
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通讯作者：
T. N. Tonkin
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作者：
T. N. Tonkin
20 世纪和 21 世纪最近的气候改善刺激了全球冰川的退缩。山谷冰川形成的冰碛提供了它们过去对气候强迫反应的沉积记录。尽管利用冰碛来了解前冰川的特征和行为，但我们对冰碛发育的了解仍然缺乏，很大程度上是由于研究活跃冰碛形成的机会有限。本论文报告了两个北极冰川（斯瓦尔巴群岛的奥斯特洛文布林冰川和瑞典的伊斯福尔斯冰川）和一个高山冰川（瑞士的施瓦茨贝格莱彻冰川）的侧额冰碛的内部结构和沉积成分，并帮助了解其古环境意义。使用探地雷达（GPR）和浅层挖掘记录了北极侧额冰碛的内部结构和沉积结构。两个北极地点的侧额冰碛都显示在其侧部区域内含有埋冰，但在其锋部区域内不含有埋冰，尽管埋冰的体积含量和潜在来源因地点而异。因此，在完全除冰后，锋区可能在地貌记录中得到更好的保存，而侧区也可能受到除冰和斜坡过程的外部审查，可能保存较差。由于北极地区的内部结构各不相同，因此有人认为，北极多温冰川形成地貌的过程在北极高海拔地区和斯堪的纳维亚大陆地区有所不同。北极侧额冰碛也与高山地区发现的冰碛不同，后者组织成堆叠的硅石单元，从冰川侧缘倾斜。对北极和高山侧额冰碛的沉积特征进行了研究和比较。研究的所有冰碛都表现出碎屑形式的梯度，这被解释为与北极和高山山谷冰川陆地系统内“主动”和“被动”碎片运输机制的相对重要性和空间变化有关。然而，冰碛形成的气候、冰川和地形状况会影响最终的地貌特征。通过重复摄影测量地形调查，研究了奥斯特洛文布林 (Austre Lovenbreen) 退化冰芯冰碛的演化过程。残余冰川冰正在经历适度的退化，主要是通过减少浪费，并且有可能作为前北极冰川特征的档案而被保存下来。本论文还有助于扩大与使用无人机（UAV）和“运动结构”（SfM）摄影测量进行地貌研究相关的更广泛的知识体系。这项研究采用的多技术方法使人们能够更好地理解冰河谷陆地系统中额侧冰碛子集（“控制型”、“奥斯特雷姆型”和“高山型”）的冰川学意义。提出了解释地貌发育的概念模型，并帮助第四纪研究寻求识别和使用侧额冰碛来确定过去冰川活动的年代和确定古冰川特征。
Recent climatic amelioration during the 20th and 21st centuries has stimulated the recession of glaciers world-wide. Moraines developed by valley glaciers provide a sedimentary record of their past response to climatic forcing. Despite the use of moraines for understanding the character and behaviour of former glaciers, our understanding of moraine development is lacking largely due to limited opportunities to study active moraine formation. This thesis reports on internal structure and sedimentary composition of lateral-frontal moraine at two Arctic (Austre Lovenbreen, Svalbard and Isfallsglaciaren, Sweden) glaciers and one Alpine (Schwarzberggletscher, Switzerland) glacier and aids understanding of their palaeo-environmental significance. The internal structure and sedimentary architecture of Arctic lateral-frontal moraine is documented using ground penetrating radar (GPR) and via shallow excavation. Lateral-frontal moraine at both Arctic sites are shown to contain buried ice within their lateral zones, but not within their frontal zones, although the volumetric content of the buried ice and potential origin varies between sites. Frontal zones are therefore likely to be better preserved in the geomorphological record following complete de-icing, whereas lateral zones, which may also be subject to de-icing and external censoring from slope processes, may be poorly preserved. As the internal structure is dissimilar across Arctic sites, it is argued that the processes involved in the development of landforms by Arctic polythermal glaciers vary between high-Arctic and continental Scandinavian settings. Arctic lateral-frontal moraine are also distinct from those found at Alpine sites which are organised into stacked diamicton units that dip away from the lateral margin of the glacier. The sedimentary signature of Arctic and Alpine lateral-frontal moraine are investigated and compared. All moraines investigated exhibit clast-form gradients which is interpreted to relate to the relative significance and spatial variation of ‘active’ and ‘passive’ debris transport mechanisms within Arctic and Alpine valley glacier landsystems. However, the climatic, glaciological, and topographic regimes in which the moraines form influence the resulting character of the landform. The evolution of a degrading ice-cored moraine at Austre Lovenbreen is investigated using repeat photogrammetric topographic surveys. Relict glacier ice is undergoing moderate rates of degradation, predominately via down-wastage and could potentially be preserved as an archive of former high-Arctic glacier characteristics. This thesis also contributes to the wider body of knowledge in relation to the use of unmanned aerial vehicles (UAVs) and ‘Structure-from-Motion’ (SfM) photogrammetry for geomorphological research. The multi-technique approach employed by this research has allowed for the glaciological significance of subsets of lateral-frontal moraine (‘Controlled’, ‘Ostrem’ and ‘Alpine’ type) within in glaciated valley landsystem to be better understood. Conceptual models accounting for landform development are presented and aid Quaternary studies that seek to identify and use lateral-frontal moraine for dating past glacier activity and determining palaeo-glacier characteristics.