High resolution geophysical study of Lake Maninjau, West Sumatra, Indonesia

Lacustrine sediments that fill volcanic craters like Lake Maninjau in West Sumatra (Indonesia) are pristine archives of past natural geological processes such as flooding, slope failure induced landslides, and volcanic eruptions. The aim of the study is to investigate the shape, and distribution of the morphological features found on the floor of Lake Maninjau as well as attempt the seismic stratigraphy of its basin fill. This is achieved by utilizing a 2-16 KHz Sub Bottom Profile seismic reflection survey that is complemented with a high-resolution sonar scanning (bathymetry) of Lake Maninjau.

The results show that the floor of Lake Maninjau is flat (~8 km wide) and reaches a maximum depth of ~168 m at the lake depocenter. Shallow sediment cores show that hemipelagic sediments predominantly cover its floor. The lake floor physiography is divided into five provinces (shelf, plateau, lake shoulder and slope, central sub-basin, and southern sub-basin), that are characterized by different morphological features with distinct responses on seismic data. These features include Mass Wasting Complexes (MWCs), blocks, gully-like features, and a lake-center dome. The MWCs are found in the northern, southern, and southeastern parts of the lake, and are occasionally characterized by embedded ~0.9-0.4 m high blocks that are interpreted to result from debris avalanches possibly accompanying earthquakes or extreme climate events. Debris flow sediments are identified on the sediments of the slope and basin shoulders, which are represented by locally constrained chaotic reflections that exhibit synchronicity. A central dome is well identified and interpreted to be of volcanic origin and may indicate a reactivation of the Maninjau volcano. The basin lacustrine infill consists of five seismic facies that serve to identify six seismic stratigraphic seismic units (SU I to SU VI), with each representing a distinctive phase in the lake evolution.

This study gives insights into the morphology and distribution of sub-lacustrine features identified within the basin fill of Lake Maninjau. It further confirms that Lake Maninjau archives past natural processes and lays the foundation for an improved understanding of the provenance of sediments and possible future utilization of the lake archive as a record of both environmental and climate change.