Volcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record

Abstract

Lacustrine sediments are particularly sensitive to modifications within the lake catchment. In a volcanic area, sedimentation rates are directly affected by the history of the volcano and its eruptions. Here, we investigate the impact of Mt. Fuji Volcano (Japan) on Lake Motosu and its watershed. The lacustrine infill is studied by combining seismic reflection profiles and sediment cores. We show evidence of changes in sedimentation patterns during the depositional history of Lake Motosu. The frequency of large mass-transport deposits recorded within the lake decreases over the Holocene. Before~8000 cal yr BP, large sublacustrine landslides and turbidites were filling the lacustrine depression. After 8000 cal yr BP, only one large sublacustrine landslide was recorded. The change in sedimentation pattern coincides with a change in sediment accumulation rate. Over the last 8000 cal yr BP, the sediment accumulation rate was not sufficient enough to produce large sublacustrine slope failures. Consequently, the frequency of large masstransport deposits decreased and only turbidites resulting from surficial slope reworking occurred. These constitute the main sedimentary infill of the deep basin. We link the change in sediment accumulation rate with (i) climate and vegetation changes; and (ii) the Mt. Fuji eruptions which affected the Lake Motosu watershed by reducing its size and strongly modified its topography. Moreover, this study highlights that the deposition of turbidites in the deep basin of Lake Motosu is mainly controlled by the paleobathymetry of the lakefloor. Two large mass-transport deposits, occurring around~8000 cal yr BP and~2000 cal yr BP respectively, modified the paleobathymetry of the lakefloor and therefore changed the turbidite depositional pattern of Lake Motosu.

Mt. Fuji Holocene eruption history reconstructed from proximal lake sediments and high-density radiocarbon dating

“…Geochemistry of glass shards from MOT15-2 (red, this study). A and B) K 2 O versus TiO 2 and K 2 O versus SiO 2 for the 1.915-mcd pumice compared to data from shards collected proximal to the Kawagodaira (Kg) caldera (blue, this study), shards from Site MOT15-1 (orange, Lamair et al, 2018), and from Lake Suigetsu (black, McLean et al, 2018). C and D) The same for the 3.455-mcd pumice (red, this study) compared to proximal shards from the Kikai-Akahoya (K-Ah) eruption (blue, this study; gray, Smith et al, 2013;cyan, Machida and Arai, 2003) and distal shards subsampled from Lake Suigetsu sediment cores (black, Smith et al, 2013).…”

“…10). However, Lamair et al (2018) geochemically analyzed scoria deposited in Lake Motosu and interpreted that it is sourced from Mt. Fuji.…”

“…We therefore focus on a much longer, apparently continuous record recovered from Lake Motosu (Site MOT15-2) that is dated at centennial-resolution and contains five scoria-fall layers deposited over the past~3000 years. Lake Motosu preserves records of paleoenvironmental change, seismic activity, and volcanic eruptions (e.g., Lamair et al, 2018), and with a Westerly relative position, upstream of the prevailing wind direction, it is positioned to record Western flank eruptions and several of the larger summit eruptions. To date, relatively few scoria-fall deposits have been identified along the Northwestern flank of the volcano (Yamamoto et al, 2005b).…”

A Review of Event Deposits in Lake Sediments

“…In the case of (finely) laminated sediments that exhibit marked color variations, visual core correlation can be achieved down to millimeter-scale accuracy (Figure 11A,B; [18,23,39,86]). Alternatively, (near-)continuous scanning or logging data, such as XRF, magnetic susceptibility, or X-ray computed tomography (CT), can be used to correlate gradual or abrupt variations through time of the background sediments (Figure 11C [19,102,174]). Additionally, independent (varve-counted) age models for each single core have allowed the correlation of cores within a lake basin [175].…”

Lake water dissolved inorganic carbon dynamics revealed from monthly measurements of radiocarbon in the Fuji Five Lakes, Japan

“…Previous studies collected sediment cores from Lake Motosu to study past environmental changes in the region (Lamair et al, 2018(Lamair et al, , 2019Obrochta et al, 2018). Obrochta et al (2018) measured radiocarbon in TOC from sediments, and they reported a D 14 C surface value of D 14 C of -41 + 2.5‰.…”