17:15 〜 18:45
[HTT15-P01] Morphological Analysis of Alluvial Fans in Northern Luzon, Philippines
キーワード：alluvial fans、geomorphology、Solsona Basin、Philippines
The Solsona Basin is a low-lying region in northern Luzon that developed from various stages of tectonic deformation along two parallel sinistral faults of the Philippine Fault Zone. East of the basin, Quaternary alluvial fans have been reported with an average slope of about 1.1°. To understand the various factors affecting the formation of alluvial fans in this tectonically active region, we determined their geometry and other morphological characteristics using a 5-m resolution IFSAR DEM and GIS. The morphometric characteristics of source catchments were also derived to explain the underlying controls (e.g., lithology, tectonics, climate) that affect the morphology of alluvial fans in this region.
Several distinct alluvial fans were recognized along the foothills that border the Solsona Basin to the east. The area of alluvial fans (Af) ranges from 4 to more than 50 km2, while the area of source catchments (Ac) ranges from 10 to 150 km2. The initial correlation of Af and Ac values shows a non-linear relationship between the area of an alluvial fan and the area of its source catchment (i.e., fan size does not necessarily increase as the catchment size increases). From DEM-based measurements, the average slope of alluvial fans and their source catchments are 3.5° and 29.8°, respectively. Source catchments with relatively higher average slopes also have more first-order streams and higher stream length total. From the alluvial fan toe to the drainage divide, the average slope of the longitudinal profiles ranges from 4.5° to 7.6°. While still preliminary, these geometric and morphological attributes of alluvial fans and their source catchments provide fundamental information for understanding the various processes that influence the formation and development of these terrestrial deposits in the Solsona Basin. Future work will explore the utility of other morphometric indices and analysis of alluvial fans in other parts of Luzon Island.
Several distinct alluvial fans were recognized along the foothills that border the Solsona Basin to the east. The area of alluvial fans (Af) ranges from 4 to more than 50 km2, while the area of source catchments (Ac) ranges from 10 to 150 km2. The initial correlation of Af and Ac values shows a non-linear relationship between the area of an alluvial fan and the area of its source catchment (i.e., fan size does not necessarily increase as the catchment size increases). From DEM-based measurements, the average slope of alluvial fans and their source catchments are 3.5° and 29.8°, respectively. Source catchments with relatively higher average slopes also have more first-order streams and higher stream length total. From the alluvial fan toe to the drainage divide, the average slope of the longitudinal profiles ranges from 4.5° to 7.6°. While still preliminary, these geometric and morphological attributes of alluvial fans and their source catchments provide fundamental information for understanding the various processes that influence the formation and development of these terrestrial deposits in the Solsona Basin. Future work will explore the utility of other morphometric indices and analysis of alluvial fans in other parts of Luzon Island.