Could road constructions be more disastrous than an earthquake in terms of landsliding?

Roads can have a significant impact on the frequency of mass wasting events in mountainous areas. However, characterizing the extent and pervasiveness of landslides over time rarely been documented due to limitations in available data sources to consistently map such events. We observed and mapped landslides for a ten year window in Arhavi, Turkey. During the same period and for the same area, we also monitored the evolution of a road network and assessed its effect on slope stability. This has been done by interpreting satellite images collected at medium to high temporal frequency (i.e., from a few months to a year) and by interviewing local people. The main road construction projects run in the area are associated with a hydroelectric power plant as well as other road extension works and are clearly associated with the vast majority (90.1%) of mass movements in the area. We also notice that the overall number and size of the landslides is much larger than in the naturally-occurring comparison area. This marks a strong and negative effect of human activities on the natural course of earth surface processes. We demonstrate this to be valid even in comparison to some of the disastrous co-seismic landslide events in recent history. Our finding show that the damage generated by the road construction is compatible with the possible effect of a theoretical earthquake with a magnitude greater than M_w=6. Overall, better co- and post-construction conditions should be ensured during and after road works to mitigate the risk to local communities. We also notice a large variation in the sediment transport as a result of road construction. This has clear implications in the sediment budget at the catchment scale, and could lead to dams in narrow sections of the river network, thus inducing variations even in the hydrological regimes. As a result, our study fits in the big picture of Anthropocene related changes and specifically points out at problems in mountainous areas that could certainly be better managed to reduce the risk to local communities.