澳洲麦考瑞assignment代写 地理冰川线理

Keywords:澳洲麦考瑞assignment代写 地理冰川线理

A区和C区均以特大尺度冰川线理(MSGLs)为主要冰下地貌。如图2.2和图2.4所示，在高分辨率hillshade栅格上可以清楚地看到“平行形成的脊沟特征”(Jakobson et al.， 2012)。MSGLs可以定义为“长度在10,000到100,000米之间的线性形式，这是最容易从航空照片或卫星图像中观察到的”(Clark, 1993)。这些小冰柱据说是由德拉姆斯冰柱形成的，因为它们更大更长，而且它们为曾经有快速冰流的地区提供了证据。关于MSGLs的形成提出了几种理论，但由于冰动力学的复杂性，没有一种理论被广泛接受。Shaw等人提出了MSGLs是由湍流融水侵蚀形成的观点，然而，现代观测表明，冰原的河床是在没有融水泛滥的情况下形成的。另一种理论是“床层变形模型”，该模型认为，由于上覆冰对沉积物施加剪应力，使软弱的沉积物发生变形，从而形成了MSGLs。但这一理论不能解释drumlins和MSGLs形成的模式现象。不稳定性理论是最广泛接受的，虽然它不能解释所有的形成方面，是由印度德马什在1998年提出的。它指出，冰和冰下沉积物的耦合流动可能具有内在的不稳定性，因此冰碛表面可能会自发地形成波浪，并以特定的波长生长。这意味着，具有不同物理性质的材料层容易发生不稳定性(不稳定性被称为在一个系统中，当小的不规则自发地生长，产生规则的模式，在这种情况下，MSGLs)。这一理论还没有得到足够的研究来得出是否这就是MSGLs形成的结论。这些理论，加上其他的，是激烈的争论，所以MSGL的形成仍然是非常未知的。由于MSGLs与快速流动的冰流相联系的重要性，对它们如何形成的认识的提高将导致影响冰的速度和流量的基本过程的重大进展。这需要在南极周围发现的MSGLs上进行进一步的研究，而不仅仅是在坑里，以促进知识的进步。
澳洲麦考瑞assignment代写 地理冰川线理
In both Area A and Area C, Mega Scale Glacial Lineation’s (MSGLs) were identified as the main subglacial landform. As shown in Fig 2.2 and Fig 2.4, they can be seen clearly on the high-resolution hillshade raster as ‘ridge-groove features formed in parallel patterns’ (Jakobson et al., 2012). MSGLs can be defined as “linear forms 10,000 to 100,000 m in length, which are most easily observed from aerial photographs or satellite images” (Clark, 1993). These MSGLs are said to have been formed from drumlins, as they are much larger and more elongated, and they provide evidence for areas in which there was a fast ice streamflow. Several theories as to how MSGLs form have been put forward but not one solution has been widely accepted due to the complexity of ice dynamics. Shaw et al. present the idea that MSGLs have been formed through erosion by turbulent meltwater flow however modern observations show that ice-sheet bedforms were created without meltwater floods. Another theory is the “bed deformation model” by that shows that MSGLs were formed through weak sediments being deformed by shear stress imparted on the sediment by the overlying ice. But this theory cannot explain the pattern phenomena through which drumlins and MSGLs form. The instability theory which is the most widely accepted, even though it cannot explain all formation aspects, was presented by Hindmarsh in 1998. It states that the coupled flow of ice and subglacial sediment may be inherently unstable, such that the ice-till surface could become spontaneously wavy with growth at a preferred wavelength. It implies that layers of materials with varying physical properties are prone to the development of instabilities (instabilities being said to occur in a system when small irregularities spontaneously grow to produce regular patterns, in this case, MSGLs). This theory has not been researched enough to conclude whether this is how MSGLs are formed. These theories, plus others, are heavily contested and so MSGL formation is still very much unknown. Due to the importance of the presence of MSGLs linking to fast-flowing ice streams, improved knowledge of how they are formed would result in major advancement of the basal processes that impact on ice velocity and flow. This entails further research being carried out on MSGLs identified around the Antarctic, not just in the PIT, to facilitate this advancement in knowledge.