Grain size and sedimentation process in the Anak Krakatau coastal area of Indonesia

Abstract

Anak Krakatau coastal area was used as a research location because it has unique characteristics, i.e., a small volcanic island with an active volcano. This study aims to analyze the grain size and sedimentation process in the Anak Krakatau coastal area. A total of 24 samples, each consisting of 8 sediment samples on land, beaches, and seabed surfaces, were collected purposively. Granulometric analysis was performed using statistical methods with Gradistat. Descriptive analysis, Linear Discriminant Analysis (LDA), and Stewart and Passega's diagrams were conducted to compare differences in grain size of sediments on land, beach, and seabed surfaces, as well as the factors that can influence them. Our results demonstrated that the mean value indicated a predominance of very coarse particles, suggesting high-energy conditions during sediment deposition. Samples from the land exhibited the largest mean size (Mz-3.627 or medium gravel), while samples from the seabed surface had the smallest mean size (Mz0.692 or coarse sand), implying greater energy on the land compared to the sea. LDA plots confirmed that sediments from the land and shore were deposited in a fluvial environment, whereas samples from the seabed represented shallow ocean deposits. Additionally, Stewart and Passega's diagrams show that seabed surface samples had been deposited through rolling action caused by waves.

Keywords

• Granulometric
• Distribution
• Sediment
• Small volcanic island
• Anak Krakatau