Predicting multi-hazard evacuation bottlenecks under built-up land expansion: A spatio-temporal network analysis on mount Gamalama, Ternate island

Maulana, Muhammad Sobri and Pratiwi, Dwitia and Prayogi, Arditya (2026) Predicting multi-hazard evacuation bottlenecks under built-up land expansion: A spatio-temporal network analysis on mount Gamalama, Ternate island. Journal of Geospatial Science and Analytics, 2 (2). pp. 109-126. ISSN 3090-8086

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Abstract

Ternate Island is a densely populated small volcanic island where urban growth increasingly extends from the coastal belt into slope and transition zones around Mount Gamalama. Although previous studies in Ternate have separately examined land-cover change, eruption hazard, landslide susceptibility, preparedness, and evacuation routes, limited attention has been given to how future built-up expansion may reshape multi-hazard evacuation performance. This study predicts the emergence of evacuation bottlenecks caused by built-up land expansion during 2025-2055 on the slopes of Gamalama using spatio-temporal network analysis. Multi-temporal Landsat and Sentinel imagery, DEMNAS, hazard-zone maps, road network data, shelter locations, public facilities, and population data were integrated within a Cellular Automata-Markov built-up growth model and a geographic information system network model. Continuous standardized exposure surfaces for volcanic eruption, rain-triggered lahar, and landslide were overlaid with current and projected settlement patterns for 2025, 2035, 2045, and 2055. Evacuation performance was evaluated using travel time to shelter, accessibility loss under hazard, route redundancy, road-segment vulnerability, and evacuation load concentration, which were synthesized into a bottleneck index. The modeled results indicate continued infill and upslope expansion along road-accessible corridors, increasing the share of built-up land located in moderate-to-high hazard zones and concentrating evacuation demand on a limited number of collector roads. Bottlenecks intensify most strongly on the west and northwest flanks and at transition nodes linking slope settlements to the coastal ring road. The study contributes an integrated framework that links urban growth projection, hazard overlay, and dynamic evacuation accessibility for a densely populated small volcanic island and provides operational inputs for risk-sensitive zoning, corridor upgrading, shelter placement, and staged evacuation planning in Ternate.

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