Sediment Deposits Texture Analysis of Besuk Kobokan River in the Northern Slope Semeru Volcano Lumajang

The flow of volcanic material from Semeru Volcano as one of the most active volcano on Java Island is still flowing and deposited along the Besuk Kobokan River which empties into Bambang Beach, Lumajang. The sediments as volcanic products are transported through the river environment with water as its transport agent. This transportation and deposition process has certain grain texture characteristics that can be identified through granulometry analysis. Geological observations and sediment sampling were carried out at 8 points along the Besuk Kobokan River. Granulometry analysis aims to identify the grain texture distribution of Semeru Volcano sediments that have been transported. The results of granulometric analysis that can identify the distribution of grain texture show that the first point to the fifth point at the sampling location was influenced by lahars flow and pyroclastic flow, resulting in randomness in grain size and rock texture. While the sixth to eighth points show the fluvial sedimentation process.