Extreme rainfall induced landslides and landscape evolution in the mountainous region of Rio de Janeiro state, SE-Brazil: geochronological and paleoenvironmental evidences.

Shallow planar landslides are common phenomena in the mountainous region of Rio de Janeiro, constituting natural hazards that can result in catastrophic disasters such as the landslides in January 2011 and February 2022 in the cities of Nova Friburgo, Teresópolis and Petrópolis in the state of Rio de Janeiro. The study here presented provides geochronological evidence of the recurrence of landslides in this region during the Holocene and the paleoenvironmental conditions associated with bioclimatic changes, evidencing the influence of extreme events on the evolution of this mountainous landscape. The geochronological analysis of these past events was obtained from the survey of organic paleosols interspersed in colluvial sequences. All radiocarbon ages found in colluvial deposits were calibrated using the SHCAL 20 curve and depositional chronological models were applied using the Oxcal software (version 4.4). Two depositional models were used, considering the random (P_sequence) or uniform (U_Sequence) deposition process from the crossing of sedimentological information. The geochronological results of colluvial deposits with the presence of superimposed organic paleosols indicate a progressive evolutionary behavior, marked by episodes of landslides and correlate deposits between 8,990 ± 40 to 856 ± 46 yrs BP from base to top, with recurrence intervals on the order of a few hundred years, ranging between 300 and 600 years. The analysis of carbon isotopes (δ¹³C) information together with palynological data indicate significant vegetation transformations in the area as well as the incidence of natural fires preceding the occurrence of landslides. The detonation of landslides after the occurrence of fires and burning of vegetation still occurs today, however, with recurrence intervals that can be less than 10 years in the same area.