Multitemporal landslide inventory analysis of an intertropical mountain in west-central Mexico——Basis for hazard management

Landslides in intertropical mountainous areas of Mexico are a natural hazard that could potentially generate a disaster. Despite this, many areas lack landslide inventories, making it difficult to monitor and efficiently manage the associated risks for local populations. For this reason, the aim of this research was to undertake a multitemporal landslide inventory and analyze its conditioning factors in the Pico de Tancítaro stratovolcano, which, in recent decades, has presented several high-risk geomorphological events with disastrous consequences for nearby localities. The spatial distribution of landslides and its conditioning factors were mapped at a 1:50,000 scale for the 1995-2020 period, through visual interpretation of orthophotos and satellite images(Landsat, SPOT, and SENTINEL). The conditioning factors that link the most to landslides were Quaternary andesite and basaltic andesite rocks;volcanic cones, mountain river valleys, and very steep to steep slopes(30° to >45°), oriented to the South, North, and East;Andosols and Leptosols;and the oyamel fir and mixed forests. 505 landslide events classified into slides and flows that occurred in 1995, 2004, 2010, and 2015 were identified. New scars generated by the reactivation of landslide processes were also observed. The landslides in the study area were triggered by torrential rains caused by hurricanes and tropical storms;such as hurricanes Alex and Patricia. The inventory and analysis of conditioning factors highlighted the distribution and dynamics of slides and flows in the study area. In addition, the most important factors for studies of landslide susceptibility, hazards, and risks in the Pico de Tancítaro stratovolcano were identified, contributing to the management of geomorphological risks in intertropical mountain areas.

Evolution History of Gassan Volcano, Northeast Japan Arc

Evolution history of the volcano is essential not only to characterize the volcano, but also consider magma genesis beneath the volcano. Most of the stratovolcanoes in northeast Japan follow a general evolutional course: cone building, horse-shoe shaped caldera forming collapse, and post-caldera stages. However, the detailed history of each stage is not well investigated. We investigated evolution history of young edifice of Gassan volcano, representative stratovolcano in rear side of northeast Japan arc. Most of the products are lavas, which are divided into two groups by geomorphologic and geologic features. The former (Gassan lower lavas) is composed of relatively thin and fluidal lavas, whose original geomorphology remains a little, while the latter (Gassan upper lavas) is composed of relatively thick and viscous lavas, whose original geomorphology is moderately preserved. Based on geologic features, the upper lavas can be further divided into Gassan upper north lavas and upper summit lavas in ascending order. After the formation of the thick lavas, horse-shoe shaped caldera was formed by the instability of the edifice, probably triggered by fault activity. No evidence of post caldera activity inner part of it is observed. Based on K-Ar data, estimated age of Gassan lower lavas is ca. 0.75 to ca. 0.6 Ma, those of Gassan upper north and upper summit lavas are ca. 0.60 to ca. 0.55 Ma and ca. 0.55 to ca. 0.45 Ma. The eruption rate is estimated to be ca. 0.0004 km3/1000 years in Gassan lower lavas and ca. 0.02 km3/1000 years in Gassan upper summit lavas. These values are lower than the eruption rate of representative Japanese stratovolcanoes.