Mount Fuji is divided by both time and composition. The
ancient mountain, Kofuji, is composed primarily of impermeable mudflows. The
modern volcano, Shinfuji, resulted from layers of basaltic lava flows and
volcanic ash. Due to its basaltic nature, the porous rock of Mount Fuji is an excellent
aquifer.
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Komitake and Ashitaka preceded Mount Fuji and through time became part of Fuji's base. Kofuji is primarily composed of tephra, versus Shinfuji which developed from massive lava flows.
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This image depicts how Shinfuji developed around Kofuji. Shinfuji most likely began as a rhyolite dome in Kofuji's crater, which grew through the build up of lava flows. The lava flows laid down layers of basalt, which has a high porosity. This allows surface runoff to seep into joints and fissures to create aquifers.
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When precipitation falls on Mount Fuji, the runoff flows
into the joints and fissures of the Shinfuji deposits until it meets the
hydrologic barrier of the Kofuji mudflow layer. The water slowly filters through
the volcanic rock. The clean water then seeps from the rock to form springs
such as Wakutama Pond, Kakita River Spring, and Kohama Pond. Water cascades
from a gap between lava layers, creating Shiraito Falls. Shiraito Falls feeds
the flow of Shiba River, acting as baseflow to a stream.
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The hydrologic cycle illustrates the movement of water through earth's system. It is estimated that 2.2 billion tons of rain and snow fall on Mount Fuji every year. After evaporation, about 4.5 million tons of groundwater are stored each day. The precipitation percolates through the volcanic rock and enters the aquifer. When the aquifer is full, the water spills out through landforms such as springs. It then flows into lakes and rivers, and eventually out to the ocean.
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This photo distinctly shows the water of Shiraito Falls flowing from between rock layers. Shiraito Falls is the baseflow for the Shiba River, which is a tributary of the Arakawa River.
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When Shinfuji formed, lava flows blocked drainage pathways and
trapped water, eventually creating five lakes. Now, exposed lava tubes act as
pipes directing runoff into the lakes and other hydrologic features of Mount
Fuji. In 864 AD, the Aokigahara lava flow split Lake Senoumi into lakes Motosu
and Sai and crept into Lake Shoji. These three bodies of water share the same
source and therefore cycle at the same rate due to the movement of groundwater
through the lava.
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This picture characterizes the age and paths of various lava flows. The lava flow which split Lake Senoumi is relatively new. This process illustrates the ease with which lava cuts off drainage pathways. It should be noted that the same lava flow leads directly to lakes Motosu, Shoji, and Sai, adding evidence that the three lakes share a water source.
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The lakes are directly in line with the lava flows, suggesting that the water which flows through the closest lava flow feeds the lake. This map shows the relation of the lakes to Mount Fuji.
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Mount Fuji has three main aquifers: the superficial, the New
Fuji Lava, and the Old Fuji aquifers. Vertical movement of groundwater mixes
the pure water of the Old Fuji aquifer with newly recharged and polluted water
from the New Fuji Lava and superficial aquifers. Anthropogenic wells in the
area allow salt water from Suruga Bay to penetrate the groundwater, leading to
further contamination. This water is used for agriculture, industry and
recreational activities. Increasing pollution at all groundwater levels may
lead to the water being unsuitable for human consumption.
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| https://www.jstage.jst.go.jp/article/hrl/5/0/5_0_58/_pdf
What is shown in this illustration: 1) The superficial aquifer occurring either in the alluvial deposits (close to the lowland) or in the surface volcanic ash beds (on the slope area), 2) The aquifer residing in the older lava flow of the New Fuji Lava Aquifer and 3) The Old Fuji Aquifer residing in the pyroclastic mudflow deposits of the Old Fuji Aquifer. "Tsuchi (2007) stated that during the solidification of basaltic lavas, the surface and the bottom of the lava flow are cooled rapidly, and crushed (https://www.jstage.jst.go.jp/article/hrl/5/0/5_0_58/_pdf)." These crushed and permeable parts are called clinkers, which allow groundwater to flow through lava. Due to the permeabilty of the clinkers,and the proclivity of basalt to fracture and fissure, paths form through the rock which separates the aquifers. This leads to vertical movement of groundwater through the rock layers and explains how pollution enters the older aquifer, contaminating what should be pure.
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| http://www.jnto.go.jp/eng/indepth/scenic/mtfuji/fuji_02.html Suruga Bay is surprisingly close to Mount Fuji. With such proximity, it is easy to understand how anthropogenic wells could contaminate the Mount Fuji aquifer with salt water. |
http://www.asianartmall.com/mtfujiarticle.htm
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