LiDAR detection of paleolandslides in the vicinity of the Suasselkä postglacial fault, Finnish Lapland

• LiDAR was applied to record paleolandslides associated with postglacial faulting.
• Several sets of paleolandslides were found in Kittilä area, Finnish Lapland.
• LiDAR revealed a new postglacial fault scarp west of the Kittilä village.
• Percussion drilled peat buried beneath slide debris yielded 14C of cal 5055 yr BP.
• Seismic activity has continued at least 5000 years after deglaciation.

Spatial distribution of paleolandslides coincides with postglacial faults (PGFs) in northern Fennoscandia, yet the timing of the seismic events and associated paleoslides is insufficiently known. We applied airborne LiDAR (Light Detection And Ranging) to record distribution of paleolandslides possibly associated with the known Suasselkä postglacial fault in Kittilä, western Finnish Lapland. Landslide-buried organic material was radiocarbon dated to bring insight if the landslides were generated by single high-magnitude (Mw > 7) earthquake or if seismic activity has continued through the Holocene. We found a total of four sets of previously unrecognized paleolandslides to indicate fault-activity in the Kittilä area. The size of the landslide scarps exceeded up to 250–300 m in width, up to 600 m in length and 10 m in the height of the back-wall. A previously unrecognized (tentatively PGF) scarp, 6 m in height and in conjunction with paleolandslides, was found in granite rock west of the Kittilä village. The slide debris was similar to local tills, yet the maximum electrical conductivity (σa) anisotropy was incoherent to any of the ice-flow (morphological) stages recognized through LiDAR or known fabric-sedimentary stratigraphy. We found peat/gyttja beneath 6 m of slide debris which yielded radiocarbon (14C) age of 4400 ± 35 BP (cal. 5055 yr BP). Our previous finding of landslide-buried woody remnants of birch (Betula ssp.) yielded cal. 9730 yr BP in Kittilä. These ages suggest that seismic activity has continued at least 5 ky after deglaciation.