2:05 PM - 2:25 PM
[HTT19-02] Quantitative analysis of bedrock weathering at Soya Coast, East Antarctica using the UAV-SfM
★Invited papers
Keywords:UAV-SfM, Rock Weathering
The record of the past ice sheet changes is important for the future prediction of the Antarctic ice sheet melting. The timing of the ice sheet retreat in the southern part of the Soya Coast, East Antarctica, was estimated based on the surface exposure ages at very limited places. However, the ice sheet expansion and retreat history of the ice sheet have been remain unclear. Therefore, it is important to estimate the relative exposed ages based on the degree of weathering of bedrocks in addition to the exposure ages in order to reconstruct detailed ice sheet history in this region.
In this study, we evaluate the degree of rock weathering based on detailed Digital Elevation Model (DEM), which was obtained by an Unmanned Aerial Vehicle (UAV)-Structure from Motion (SfM) analysis in the northern part (West Ongul Island) and the southern part (Telen) of the Soya coast. From these two areas, we sampled the same type of basement rocks and carried out the hardness test using the equotip hardness tester. The field survey was carried out during a December 2015 - March 2016 as a field campaign of 57th Japanese Antarctic Research Expedition. In order to identify the geomorphological characteristics in Telen and West Ongul Island, we applied two-dimensional Fourier analysis and high pass filtering (5.0 m, 1.0 m, and 0.2 m) of them for the obtained DEMs. The result shows that the low frequency component (5.0 m high pass) reflects topographical relief relating to the geological structure. On the other hand, the high frequency component (0.2 m high pass) distributions only near the steep slope. Histograms of the degree of slope for ca. 5.0 cm mesh reveal that Telen has more steep slope (>40°) areas. These results show that the topographically angular corresponding to knick points are conserved in Telen relative to that of West Ongul Island. In other words, the topographically angular in West Ongul Island is thought to be scraped off due to weathering, suggesting the long time of exposure. In addition, Equotip rebound value (L-value) of Telen was about 1.2 times larger than that of West Ongul Island, and L-value of the sample from West Ongul Island decreases rapidly from surface to inside. These indicate that the degree of the weathering of the rock is significant in the West Ongul Island, which is consistent with the topography features revealed by DEM analysis. Therefore, the difference in topographical characteristics between the northern and southern part of the Soya Coast likely reflects the degree of weathering due to the different exposure time. However, there are various factors, which have to be addressed, such as rock type, inclination, and environment at the bottom glacier. Therefore, further efforts to find out the better approaches are needed for the quantitative analysis of bedrock weathering.
In this study, we evaluate the degree of rock weathering based on detailed Digital Elevation Model (DEM), which was obtained by an Unmanned Aerial Vehicle (UAV)-Structure from Motion (SfM) analysis in the northern part (West Ongul Island) and the southern part (Telen) of the Soya coast. From these two areas, we sampled the same type of basement rocks and carried out the hardness test using the equotip hardness tester. The field survey was carried out during a December 2015 - March 2016 as a field campaign of 57th Japanese Antarctic Research Expedition. In order to identify the geomorphological characteristics in Telen and West Ongul Island, we applied two-dimensional Fourier analysis and high pass filtering (5.0 m, 1.0 m, and 0.2 m) of them for the obtained DEMs. The result shows that the low frequency component (5.0 m high pass) reflects topographical relief relating to the geological structure. On the other hand, the high frequency component (0.2 m high pass) distributions only near the steep slope. Histograms of the degree of slope for ca. 5.0 cm mesh reveal that Telen has more steep slope (>40°) areas. These results show that the topographically angular corresponding to knick points are conserved in Telen relative to that of West Ongul Island. In other words, the topographically angular in West Ongul Island is thought to be scraped off due to weathering, suggesting the long time of exposure. In addition, Equotip rebound value (L-value) of Telen was about 1.2 times larger than that of West Ongul Island, and L-value of the sample from West Ongul Island decreases rapidly from surface to inside. These indicate that the degree of the weathering of the rock is significant in the West Ongul Island, which is consistent with the topography features revealed by DEM analysis. Therefore, the difference in topographical characteristics between the northern and southern part of the Soya Coast likely reflects the degree of weathering due to the different exposure time. However, there are various factors, which have to be addressed, such as rock type, inclination, and environment at the bottom glacier. Therefore, further efforts to find out the better approaches are needed for the quantitative analysis of bedrock weathering.