The Isopach Mapping of Volcanic Deposits of Mount Samalas 1257 AD Based on the Values of Resistivity and Physical Properties

Abstract

A detailed study had been conducted on the sediment of Mount Samalas' volcanic eruption in 1257 AD. Using the framework of the reconstruction of the ancient eruption of Mount Samalas, the first step was to map and analyze the deposits of volcanic sediment. Secondly, we analyzed the effect of geomorphology and the distance function to the isopach thickness. The results show that a combination of methods allowed to provide a high resolution map of the distribution of the thickness of the volcanic deposits, both on the slope and in alluvial areas. Geo-electric survey results (both Vertical Electric Sound (VES) and 2D mapping) show consistent changes in the pattern of contrast resistivity layer interface, for all areas. The pattern changes in a row of the top layer, the high resistivity turned into the low. Furthermore, the second and third layer interface changes from low to the high resistivity. High resistivity on the top layer is interpreted as a layer of unconsolidated volcanic sediment. High resistivity values are range from 736 to 2000 Ohm.m on the top layer in the area of the slopes while in the area of alluvial, the resistivity values range from 20 to 958 Ohm.m. Generally, the volcanic deposits in the area of the slopes have a higher value of isopach (>17 m) than in areas of alluvial (<25 m). The geomorphology seemed to have no significant effect on the isopach value, particularly pyroclastic fallout. Such is the case with distance from the source to the site, which is not linear. The value of isopach increases westward from 21 to 31 km, in contrast to the East, which began to occur at a distance of 14 km to 21 km.

Determination of Material Characteristics and Shear Wave Velocity of Volcanic Sediment Layer of Mount Samalas Using MASW Technique

“…We found several outcrops with different physical characteristics in the southern region of Mount Samalas and Mount Rinjani, so we chose the area as a research location (Figure 1). [5] found that the sediment type of Mount Samalas possesses massive, unconsolidated, unsorted, and multi-model granule size characteristic. Three basic types of classtic sediment of volcanic are: falls, surges, and PDC sediments [6].…”

“…Volcanic classtic deposits of Mount Samalas can be found in all parts of Lombok Island [5]. The eruption of the eruption of Mount Samalas, particularly in the South and Southwest regions, has composition: Alluvium (Qa), Young volcanic rock (Qhv), Lokopiko (Qvl), and Kalibabak Formation (Tqb) ( Figure 1).…”

Determination and Mapping of the Causes of High Risk of Earthquake Hazards Using Geoelectrical Data in Bengkaung, Batu Layar, West Lombok Indonesia

“…Under the pumice layer there is a layer of breccia sand that covers the clay layer below (Paleo-topography). This layer of quicksand and breccia covers almost the entire island of Lombok (Hiden et al, 2014;Hiden et al, 2017).…”

Species and potential sources of phosphorus in groundwater in and around Mataram City, Lombok Island, Indonesia

“…The third layer is silt and fine sand saturated with water and occurs at an average depth of 39 m from the ground surface. The third layer, which began at a depth of 47 m from the ground surface, is interpreted as the bedrock consisting of sandstone and mudstone [25]. The rock that made up the layers of the bed of the volcanic deposits included clay, gravel, pumice sand, sand, rough pumice granules, silt, and fine black sand [25].…”