The mass balance in a caldera lake and new ponds, produced by a volcanic eruption

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We monitored flow velocity, water turbidity and water temperature and trapped suspended sediment in Lake Toya for July to October 2001 and for March to August 2002. As a result, we did not find the highly, turbid bottom layer in the lake, which was produced and retained by the mudflows for April to October 2000. The depletion of the turbid layer is due to the gravitational settling of suspended sediment.A crater pond (N-12 or N-19) and a new pond (Izumi Pond), produced by the 2000 eruption of Usu Volcano, were hydrologically examined for July to November 2001 and for April 2002 to February 2003, respectively. An estimate of water budget in the ponds gave the net groundwater output at 0.003 to 0.004m^3/s in lzumi Pond and 0.00005m^3/s in N-19 Pond. This indicates that the water output by evaporation rather than the groundwater output prevails in the crater pond.