Terminus Dynamics and Active Deformation of Proglacial Sediments at an Advancing Glacier: Taku Glacier, Alaska

Motyka00221307塔库冰川在过去的几十年里一直在稳步推进，挖掘它的冰床，并将自己挖成冰川、河流、潮汐、沉积物和冰川喷发沉积。这种推进的原因与“潮水冰川循环”的推进阶段有关。在20世纪的大部分时间里，19世纪的崩解退缩导致了高的面积积累比(AAR)(~0.90)。由于冰川和河流沉积物充填了峡湾，导致AAR很高，冰解作用逐渐减少，导致数十年来净平衡为正，推动目前自1890年以来的7公里(公里)的前进。因此，塔库冰川为研究缓慢的冰川进入软质沉积物提供了一个理想的环境和难得的机会。终点区冰层的持续增厚表明，这一进展将在未来几年内继续下去。勘察观察记录了冰川沉积物在终点处前方约200米处的同期变形，压缩沉积物中形成了高达10米的突出凸起，上覆土壤和植被发生弯曲。首席调查员将研究前进冰川末端的动力学，并调查这一前进对冰川地貌的影响。将在冰川末端和冰川地貌上测量表面速度、应变率和表面高程变化，同时测量末端位置的变化。将使用探地雷达(GPR)和无线电回波测深(RES)来确定冰川的几何形状和冰床的性质。他们将重复资源调查，以调查正在进行的冰下沉积物挖掘和挖掘。探地雷达还将用于绘制冰川沉积物结构及其变形的三维图像。沉积物上现有的和新的标记将测量运动和应变。这项研究的一个主要特点是使用精确的全球定位系统在几个月的时间里同时测量冰端冰速和冰川沉积物的短期变化。末端动力学和物质平衡是冰川响应理论的组成部分，但人们对它们知之甚少。首席调查员将使用有限元分析，以应变数据和几何形状为约束，调查末端冰楔以及次冰川和冰川沉积物的变形和应力场。他们的目的是了解末端推进的详细动力学以及末端附近沉积物和冰的流变性。他们还将利用我们持续的航空高程测量和地面高度的摄影测量，研究冰川增厚和末端推进之间的关系。

Motyka00221307Taku Glacier has been steadily advancing for the last several decades, excavating its bed and entrenching itself into glaciomarine, fluvial, tidal, sediments and glacier outwash deposits. The cause of this advance is related to the advance phase of the "tidewater glacier cycle". A 19th century calving retreat resulted in a high area accumulation ratio (AAR) during most of the 20th century (~ 0.90). The high AAR and gradual diminishment of calving due to infilling of the fjord by glacial and fluvial sediments resulted in a positive net balance for several decades, driving the current advance 7 kilometers (km) since 1890. Taku Glacier therefore presents an ideal setting and rare opportunity for the study of slow glacier advance onto and into soft sediments. Continued thickening of ice in the terminus region indicates this advance should continue over the next several years. Reconnaissance observations have documented contemporaneous deformation of proglacial sediments about 200 meters (m) in front of the terminus and prominent bulges up to 10 m high have formed in the compressed sediments with buckling of the overlying soil and vegetation. The Principal Investigators will study the dynamics of the advancing glacier terminus and investigate the effects of this advance on the proglacial geomorphology. Surface velocities, strain rates, and surface elevation changes will be measured both on the glacier terminus and on proglacial features, along with measurements of changes in terminus position. Ground penetrating radar (GPR) and radio echo sounding (RES) will be used to define the glacier geometry and the nature of the bed. They will repeat RES surveys to investigate ongoing subglacial sediment excavation and entrenchment. GPR will also be used to develop a 3-dimensional picture of the structure of the proglacial sediments and their deformation. Existing and new markers on the sediments will measure motion and strain. A key feature of this study will be simultaneous measurement of short-term changes in terminus ice speed and proglacial sediments using precision GPS over several months. Terminus dynamics and the mass balance are integral parts of glacier response theories, but they are poorly understood. The Principal Investigators will use finite element analyses to investigate the deformation and stress fields in the terminal ice wedge and of the sub- and proglacial sediments, using strain data and geometry as constraints. Their aim is to understand the detailed dynamics of terminus advance and the rheological properties of the sediments and the ice near the terminus. They will also investigate the relation between glacier thickening and terminus advance, using our continuing airborne altimetry and photogrammetric measurements of surface elevation.