Work

Reactivated slope, perched channel, and protective-action capacity: an integrated analysis of the 2025 Matai'an landslide-dam disaster, Taiwan

Year: 2026

Type: preprint

Abstract: On 21 July 2025 the largest landslide recorded in Taiwan impounded the Matai'an Stream in eastern Taiwan; sixty-four days later the barrier overtopped and breached, and nineteen residents of Guangfu Township died after nineteen official alerts. We ask why a dense warning sequence did not convert into survivable protective action for an identifiable group, treating physical preconditioning, channel geometry and warning practice as one causal chain and not as separate literatures. Using documentary analysis with historical topographic maps, satellite imagery and an earthquake catalogue, read through a terrain-explicit extension of Cutter's Hazards-of-Place model coupled to the Protective Action Decision Model, we establish three results. The failure reactivated ground mapped as unstable since 1924 and seismically loaded by 198 earthquakes of local magnitude 5.0 or above within 50 km between 2018 and failure. A century of dike construction left the channel perched above the plain, so the flood was delivered through a single dike aperture to the lowest, most densely settled ground, while the pre-1904 Amis settlement on higher ground was largely spared. Vertical evacuation, the mode recorded for 61.5 per cent of residents, carried a reinforced-concrete two-storey condition never matched to individual addresses, and the fatalities concentrated on the lowest streets. We derive a reproducible vertical-evacuation screening threshold and argue that a protective-action instruction carries an evidentiary burden the issuing authority must discharge before an event.

Source: Research Square

DOI: 10.21203/rs.3.rs-10678671/v1