Pattern recognition of LiDAR data and sediment anisotropy advocate a polygenetic subglacial mass-flow origin for the Kemijärvi hummocky moraine field in northern Finland

Abstract

Object-based image analysis and supervised machine learning on a digital elevation model derived from airborne laser scanning data were conducted to assess the aggregate raw material potential over the Kemijärvi hummocky moraine field in Finnish Lapland. Geomorphometric analysis revealed surface stoniness to be diagnostic of moraine hummocks. It was utilized to detect true moraine hummocks from among the potential hummocks delineated using object-based image analysis with logistic regression of curvature features derived from the digital elevation model (area under the receiver operating characteristics curve, AUC = 0.77). Based on the electrical-sedimentary anisotropy data, the Kemijärvi moraine is polygenetic such that the ridges are diagonally and erosionally fluted (from sector 280–290°) on their surfaces, while the ridge cores are deposited from the NW (from sector 310–340°). The cores are composed of infill gravels and crudely stratified diamict sequences. We consider the core of the Kemijärvi hummocky moraine field to represent pre-existing (Early Weichselian) subglacial ridges rather than being generated through monogenetic (Late Weichselian) compressional shearing and stacking, frozen-bed extension, or bed ribbing instability mechanisms, as presented for ribbed moraines that are transverse to ice flow. Recently, evidence has been presented of multiple slip events (earthquakes with moment magnitudes Mw ≈ 6.7–7.0) up-ice from Kemijärvi. We therefore propose that the genesis of the hummocks may be associated with past (Early Weichselian) fault instability within glacio-isostatic adjustment(s), which was able to generate subglacial water bodies (possibly lakes) and saturated materials that were forced towards the SE. Based on this new geomorphological evidence from mapping using a digital elevation model derived from airborne laser scanning data and azimuthal conductivity surveys combined with the reinterpretation of previously presented geophysics and sedimentological observations, we suggest the Kemijärvi hummocky moraine field to be reconsidered as the Kemijärvi subglacial mass-flow field, which holds significant potential for construction aggregate materials.