11:15 AM - 11:30 AM
[HDS08-09] Hydrological structure of sedimentary rock slopes and the conditions of landslides in northern Greenland
Keywords:Greenland, Landslides, Colluvium slope, Electrical Resistivity Tomography, infrared temperature imaging
In northern Greenland's Siorapaluk, extremely large-scale landslides of the thick colluvium layer occurred frequently due to rainfall in August 2016 and August 2017. We have investigated there and analyzed geology and geomorphological characteristics since 2018, however there was a lack of information so far regarding the hydrological environment causing to landslides.
The colluvium consists of a mixture of poorly sorted sandstone and medium to coarse sand, with no heterogeneity observed. However, due to its poor sorting, rainwater was unlikely to penetrate quickly enough to cause a massive landslide. Furthermore, the landslide deposits and topography exhibited characteristics of debris avalanches due to their low water content.
For these reasons, the authors hypothesized that the reason for the landslide exists in the deep part of the colluvium layer.
In the summer of 2023, the authors investigated the internal structure of the colluvium slope and the hydrological environment on the slope using two methods. One was Electrical Resistivity Tomography (ERT) of the landslide site's longitudinal section, and the other was wide-area surface temperature investigation of the slope, including the landslide site, using a high-performance infrared temperature camera. The latter was expected to be influenced by the color of the terrain, the presence or absence of sunlight, and the presence of water springs, because the almost complete absence of vegetation on the slope.
The results obtained are as follows: The ERT revealed a low resistivity area extending over 50 meters at a depth of about 5 meters, but this did not continue across the entire landslide site, and there were places where high resistivity areas reached the surface intermittently. The low-resistivity areas were interpreted as moist, high-permeability rocks/debris, and the high-resistivity areas as low-permeability rocks/permafrost. The electrical resistivity distribution likely reflects the geological structure, suggesting that relatively fissure-free sedimentary rock layers (high resistivity areas) transverse the moist zone near the surface. Therefore, water passing through the moist zone could increase water pressure near the top of the fissure-free rock layers. This is consistent with other observational facts.
Observations with the infrared camera during cloudy weather revealed spot-like low-temperature areas. These low-temperature spots could be interpreted as water springs compared to visible light photographs. Such water springs were located on the upper parts of the long slope, scattered over the thick colluvium layer. The landslides may occur due to spot surges in water pressure.
The colluvium consists of a mixture of poorly sorted sandstone and medium to coarse sand, with no heterogeneity observed. However, due to its poor sorting, rainwater was unlikely to penetrate quickly enough to cause a massive landslide. Furthermore, the landslide deposits and topography exhibited characteristics of debris avalanches due to their low water content.
For these reasons, the authors hypothesized that the reason for the landslide exists in the deep part of the colluvium layer.
In the summer of 2023, the authors investigated the internal structure of the colluvium slope and the hydrological environment on the slope using two methods. One was Electrical Resistivity Tomography (ERT) of the landslide site's longitudinal section, and the other was wide-area surface temperature investigation of the slope, including the landslide site, using a high-performance infrared temperature camera. The latter was expected to be influenced by the color of the terrain, the presence or absence of sunlight, and the presence of water springs, because the almost complete absence of vegetation on the slope.
The results obtained are as follows: The ERT revealed a low resistivity area extending over 50 meters at a depth of about 5 meters, but this did not continue across the entire landslide site, and there were places where high resistivity areas reached the surface intermittently. The low-resistivity areas were interpreted as moist, high-permeability rocks/debris, and the high-resistivity areas as low-permeability rocks/permafrost. The electrical resistivity distribution likely reflects the geological structure, suggesting that relatively fissure-free sedimentary rock layers (high resistivity areas) transverse the moist zone near the surface. Therefore, water passing through the moist zone could increase water pressure near the top of the fissure-free rock layers. This is consistent with other observational facts.
Observations with the infrared camera during cloudy weather revealed spot-like low-temperature areas. These low-temperature spots could be interpreted as water springs compared to visible light photographs. Such water springs were located on the upper parts of the long slope, scattered over the thick colluvium layer. The landslides may occur due to spot surges in water pressure.