Development of small ice-dammed lake and its sedimentary infill (Nordenskiöldbreen, Spitsbergen)
| Autoři | |
|---|---|
| Rok publikování | 2016 |
| Druh | Konferenční abstrakty |
| Fakulta / Pracoviště MU | |
| Citace | |
| Popis | Studied temporary lake existed in the proglacial zone of Nordenskiöldbreen in the north coast of Adolfbukta between the early 90th of the 20th century up to the year 2012. The lake itself filled depression in mica schist bedrock and was bounded by the margin of the glacier. The lake can be divided into two parts separated by basement elevation (”intrabasinal high”) - east elongated depression and circular west depression. Proglacial stream entered into the east depression and continuously delivered sediment. Due to that fact, lake was almost completely filled by gravels, sands and occasionally also silts. Coarse grained Gilbert-type delta formed at the stream entry. Water from the east depression freely continued into the west depression, which was filled with thin blanket of fine grained deposits. Delta in the east depression has tripartite structure of topset, foreset, bottomset. Topset is represented by braided alluvium. Foreset beds are formed by deposits of turbidity currents and debris flows. Deposits of bottomset reflect suspension deposition, deposition from low-density turbidity currents and occasional debris flows. Deltaic deposits create four morphologically terraces. Whereas the highest and also the oldest terrace is located close to margin of the east depression, the youngest and lowest terrace is situated near the centre of the east depression. Each sedimentary terrace follows morphology of the bedrock surface, which reveals several morphological steps. Evolution of the delta was directed by bedrock morphology. Reconstruction of the lake history is possible based on sedimentary properties and results of satellite images, which delta and bedrock morphology and their areal distribution. Water level in the lake was generally stable, because the incoming water lake was drained through the gorges in the bedrock. The lake partially entered also under the glacier, which caused calving of the glacier. Especially steep - bounded concave shape of the glacier margin proclaims the lake on satellite images. Continued calving of the glacier enlarged rock depression, which was available for inundation by the lake. The lake did not grow in volume, but shifted laterally following the retreating glacier. Stepped deepening of the lake bottom towards the glacier was responsible for every decrease of the lake level (terrace) as each rock step was exposed by the retreating glacier. The lake disappeared by the complex decrease of glacier barrier. Water drained by subglacial gorge in the bedrock to Adolfbukta. Development of the lake was driven by three main factors: morphology of bedrock, stability of glacier barrier and clastic sediment delivery. |