Tatun Volcano Group is a cluster of dormant volcanoes surrounding Metropolitan Taipei. Rugged terrain, monotonic lithology and dense vegetation covers are adverse factors for mapping the geological structures. In this study, airborne Lidar survey was conducted to obtain a bare ground DEM with 2m grid and with an accuracy of decimeters. Shaded-relief images, pit-patterns and drainage networks are then derived from these DEMs for visual interpretation. 51 volcanoes are thus recognized. Two fissures running through the highest volcano in this area, namely Mount Seven-stars, are extending 2000m and 1000m, respectively. The largest width and depth of the opening of the ruptures is located in the west flank of the volcanic cone. The slope angle of the east-wing of the volcanic cone is 36°, whereas the angle of the west-wing is only 24.5°. The opening of the west fissure is larger and its extension is longer than the east one. Thus, the west side can be subjected to an active extensional process of strain. The fissures could be resulted from the ongoing regional extension of the Tatun Volcanic area due to the plate subduction and collision of the Eurasian Plate and the Philippine Sea Plate.
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