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Kuttara Volcano, Hokkaido, Japan, consists of temperate Lake Kuttara and the western Noboribetsu geothermal area. In order to explore geothermal relations between Lake Kuttara and the geothermal area, the heat budget of a hydrothermal pond, Okunoyu, was evaluated, and the heat storage change in the lower layer of Lake Kuttara was calculated by monitoring the water temperature at the deepest point. The lake water temperature consistently increased during the thermal stratification in June-November of 2013-2016. The heat flux Q(B) at lake bottom was then calculated at a range of 4.1-10.9 W/m(2), which is probably due to the leakage from a hydrothermal reservoir below the lake bottom. Meanwhile, the heat flux H-G(in) by geothermal groundwater input in Okunoyu was evaluated at 3.5-8.5 kW/m(2), which is rapidly supplied through faults from underlying hydrothermal reservoirs. With a time lag of 5 months to monthly mean Q(B) values in Lake Kuttara, the correlation with monthly mean H-G(in) in Okunoyu was significant (R-2 = 0.586; p < 0.01). Applying Darcy's law to the leakage from the hydrothermal reservoir at 260-310 m below the lake bottom, the time needed for groundwater's passage through the media 260-310 m thick was evaluated at 148-149 days (ca. 5 months). These findings suggest that the hydrothermal reservoir below lake bottom and the underlying hydrothermal reservoirs in the western geothermal area are both connected to a unique geothermal source in the deeper zone as a geothermal flow system of Kuttara Volcano.

River seepage serves as the main source of groundwater in alluvial fans. However, reasonable estimates are rarely obtainable due to inaccuracy of vertical flows around the losing river. In the alluvial fan of the Toyohira River, Japan, to provide a straightforward description of vertical hydraulic gradient (VHG), this study demonstrates assignment of constant head boundary conditions on the shallowest aquitard instead of no-flow conditions on the basement. Initial constant heads and layer-scale anisotropy are calibrated in terms of hydraulic heads. As a result, the simulated river seepage is in reasonable agreement with previous discharge measurements, with net water loss determined to be approximately 1 m(3)/s. Although the simulation fails for water gain in the lower section, due to a lack of sporadic intercalations of fine deposits, the conditioned VHG modelling approach is found to be effective on a regional scale, especially when losing/gaining sections have not been identified in advance.

Calving glaciers are rapidly retreating in many regions under the influence of ice-water interactions at the glacier front. In contrast to the numerous researches conducted on fjords in front of tidewater glaciers, very few studies have been reported on lakes in which freshwater calving glaciers terminate. To better understand ice-water interactions at the front of freshwater calving glaciers, we measured lakewater temperature, turbidity, and bathymetry near Glaciar Perito Moreno, Upsala, and Viedma, large calving glaciers of the Southern Patagonia Icefield. The thermal structures of these lakes were significantly different from those reported in glacial fjords. There was no indication of upwelling subglacial meltwater; instead, turbid and cold glacial water discharge filled the region near the lake bottom. This was because water density was controlled by suspended sediment concentrations rather than by water temperature. Near-surface wind-driven circulation reaches a depth of similar to 180 m, forming a relatively warm isothermal layer (mean temperature of similar to 5-6 degrees C at Perito Moreno, similar to 3-4 degrees C at Upsala, and similar to 6-7 degrees C at Viedma), which should convey heat energy to the ice-water interface. However, the deeper part of the glacier front is in contact with stratified cold water, implying a limited amount of melting there. In the lake in front of Glaciar Viedma, the region deeper than 120 m was filled entirely with turbid and very cold water at pressure melting temperature. Our results revealed a previously unexplored thermal structure of proglacial lakes in Patagonia, suggesting its importance in the subaqueous melting of freshwater calving glaciers.

Oikamanai Lagoon in the Tokachi coastal region of Hokkaido, Japan, opens to the ocean several times a year due to water overflow across the sand bar triggered by rainfall or snowmelt runoffs of inflowing rivers. The water-budget calculation for the lagoon under closed conditions indicates that the net groundwater output occurs as confined groundwater, probably flowing into the ocean through the sand bar. The net groundwater output is then balanced mainly by river inflow. For the lagoon's heat budget, heat flux caused by net groundwater output was an unknown factor balanced by heat flux of river inflow and a change in the lagoon's heat storage. The two net groundwater outputs from water and heat budgets exhibit the linear relationship close to the one-to-one correspondence. Hence, two unknown factors-groundwater outflow (G (out)) and groundwater inflow (G (in))-were estimated separately. G (out) and G (in) values averaged over the budget period were estimated to be 1.04 m(3) s(-1) and 0.078 m(3) s(-1) (7.5 % of G (out)), respectively. Thus, the groundwater outflow to the ocean, representing most of the groundwater output, may control water residence time and water and material cycles related to the ecosystem in or around the lagoon.

Geothermal heat fluxes into the deepest waters of four caldera lakes were measured. Temperature profiles within the stratification period between July and November 2007 allowed a quantification of the acquired heat. Due to their enormous depth, heat input from the lake bed was locally separated from heat fluxes at the surface. In conclusion, a direct measurement of geothermal heat input could be accomplished. Although enhanced geothermal activity could be suspected in all cases, two lakes showed a geothermal heat flux of 0.29 or 0.27 W/m(2) (Lake Shikotsu and Lake Tazawa), as found in other regions not affected by volcanism, while both other lakes (Lake Kuttara and Lake Towada) showed a greatly enhanced heat input of 1 or 18.6 W/m(2), respectively. In conclusion, within our investigated set, all lakes acquired more heat from the underground than the continental heat flux average. Hence, the heat flux into the lakes from the ground was not dominated by the temperature gradient implied by the inner heat of the earth. Other effects like the general temperature difference of deep lake water and the groundwater or local sources of heat in the underground deliver more important contributions. Obviously the flow of water in the underground can play a decisive role in the heat transport into the deep waters of lakes.

The water budget of a coastal lagoon, Oikamanai Lagoon, Hokkaido, Japan, sporadically opening to the Pacific Ocean, is estimated by establishing a bathymetric map of high accuracy (0.3 m depth interval), and by monitoring the meteorology, lagoon water level and river stage. The opening to the ocean is produced by incising the sand bar from the overflow and discharge of lagoon water at the lowest site of the sand bar. The overflow results from an increase of the lagoon water level basically by snowmelt or rainfall river runoffs. As a result, the drainage by the opening to the ocean caused the lagoon to decrease the water volume up to more than 96%. The estimate of the water budget at nearly constant water level under closed condition of the lagoon suggests that, as the net groundwater output from the lagoon, the confined groundwater outflow to the ocean across the sand bar prevails. The gravelly confined aquifer was inferred to be at the similar elevation with some thickness along the grave-sand bar about 2000 m long. Meanwhile, during the regrowth of the sand bar at the outlet after the opening, the gravelly sediment first deposited near the sea level. Hence, the spatial distribution of the gravelly aquifer along the sand bar suggests that the whole sand bar was simultaneously broken in the past and then was grown up again.

An ice-ridge line more than 2,000 m long was discovered in a closed, deep lake—Lake Kuttara, Hokkaido, Japan—in the ice-covered season of 1995. To clarify when and how the ice-ridge line built up, meteorology and ice and water temperatures were monitored, and the density, thermal conductivity, and thickness of the covered ice were measured from January through March 1995. The covered ice on 4 and 5 March 1995, which corresponded to the period with the thickest lake ice, consisted of snow ice 0.05- to 0.07-m thick and candle ice 0.18- to 0.21-m thick. Numerical simulations for the ice thickness and temperature were carried out using a one-dimensional, unsteady, threelayer model. The simulated results, which were reasonable to the observations, indicate that due to the ice contraction and expansion, the ice-ridge line started to construct on 2 February and was completed the next day.

In very deep freshwater lakes, deep recirculation presents itself with remarkable differences to shallower lakes. We consider the stratification where density gradients are exclusively due to temperature differences. The annual circulation patterns are discussed for various climatic conditions. Very deep lakes do not necessarily produce full overturns during Tmd transition in autumn and spring. Peculiarities of the stratification are derived for cases, in which surface temperatures cross 4℃ during the annual cycle: Firstly, the asymmetry between autumn and spring circulation, secondly, the proximity of temperature to the Tmd profile, and thirdly, the isothermal deep water. We compare conceptual model results of horizontally homogeneous lakes with measurements in very deep caldera lakes in Japan (Lakes Ikeda, Tazawa, Toya, Kuttara and Shikotsu). Between oligomictic lakes and thermobarically stratified lakes, we have found lakes circulating reliably despite their enormous depth. We discuss susceptibility to climate variability supported by comparisons with single point measurements from the 1920s and 1930s.

Hydrological characteristics of englacial and subglacial drainage systems in Gulkana Glacier, Alaska, were examined by analysing temporal variations of discharge and sediment load in the proglacial Phelan Creek in 2001. From data plots on semi-log paper, it appeared appropriate to separate both discharge and sediment load into fast and slow components. The two components were possibly produced by two different drainage systems: an englacial and subglacial, “channellized” system in the ablation zone, and a subglacial, “distributed” system in the accumulation zone. The data indicate the occurrence of an event during which part of the “distributed” drainage system changed into the “channellized” drainage system. The daily time-series of discharge and sediment load were represented using a tank model. In the model, the drainage from an additional tank was added, supposing that a subglacial reservoir full of water and sediment collapsed slowly when the subglacial drainage system changed from distributed to channellized. The simulation with the collapsed tank gave much more reasonable results than those with no collapsed tank. The contribution of the collapsed tank to total sediment load is 24%, which is much larger than 9% to total discharge. Copyright © 2006 John Wiley & Sons, Ltd.

The thermal structure of two Himalayan glacial lakes, Tsho Rolpa and Imja in the eastern Nepal, was examined by observations in the pre-monsoon seasons of 1996 and 1997. Tsho Rolpa had an isothermal mixed layer at water depths of 0–20 m, whereas Imja did not possess such an isothermal layer. This difference in the thermal structure is explained by the condition that diurnal valley winds, producing wind-driven currents, blow strongly near the water surface of Tsho Rolpa, but very weakly near that of Imja. The wind observations above or near the end moraine indicated that a daily wind system of strong, diurnal valley winds and weak, nocturnal mountain winds is common to the lakes. It was suggested that with respect to the valley winds, the weak winds near the surface of Imja result from topographic screening effects of the upwind dead-ice zone and end moraine 20–25 m higher than the water surface. In order to ascertain the topographic effects, three-dimensional numerical simulation of airflow was carried out by making topographic models of actual size in the calculation domain, corresponding to Tsho Rolpa and Imja and their surrounding topography. The simulation revealed that, when winds blow at constant velocities of 1–5 m s−1 at 2 m above the points corresponding to the weather stations, the wind velocity at 2 m above the water surface for Imja is 33–42% smaller than for Tsho Rolpa. With increasing heights of the end moraine and dead-ice zone, the wind velocity near the lake surface efficiently decreased by decreasing the lake length from 3.1 or 2.2 km to 1.2 km.

International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan., In order to limit possible inland seawater intrusion, important freshwater resources contained in coastal aquifers should be exploited carefully. Salinization of coastal waters is often due to inflow of dense saline water from the sea or deep inland geological layers, during heavy groundwater withdrawals, drought or long-term sea level rise. A continuous trend in the decrease of groundwater level and land subsidence, resulting from freshwater over-pumping, has been noticed in the subsurface of Hokkaido's coastal area facing the Sea of Japan, since the 1960's. This could lead to the decline of groundwater quality. This decline may be further amplified by seawater level increase. Past sea level records along this coast have shown continuous oscillations over various timescales of years and decades. A particularly high rate of sea level increase (3.2 mm/year) compared to the rise of the world ocean level, has been observed towards the northern edge of this coast. To avoid inland saltwater encroachment causing salt contamination of coastal aquifers, it's vital to determine the position of the seawater-freshwater interface and control its movement. For this purpose, water chemical analyses from drilled wells as well as analytical and numerical simulations are often employed to approximate the location of this boundary and understand the relevant processes that cause saltwater intrusion in coastal aquifers. For the present study, two modeling solutions are used to determine the shape and position of the interface between the landward potential seawater intrusion and subsurface freshwater outflow to the coast. Then, investigations are conducted to examine the impact of groundwater level decrease and sea level fluctuations, on the extent of this saltwater interference in the dynamics of the coastal flow system of the area.

International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan., In order to clarify the characteristics of water and sediment discharges from glacier-covered basins under maritime climate, hydrological observations were carried out within a drainage basin which contains Koryto Glacier in Kamchatka Peninsula, Russia. Water discharge of a proglacial stream near the glacier terminus varied between 3 and 12 m^3 s^[-1] during the summer of 2000. Variation in suspended sediment concentration was positively correlated with water discharge, and values of sediment concentration ranged from 1.0 to 0.1 g1^[-1]. A runoff model which consists of two linear reservoirs in series was applied to the basin for simulating discharge variation. Considering a seasonal change in glacier drainage systems, this model can simulate stream discharge well. Three different models based on rating curve, multiple regression and sediment storage for suspended sediment transport estimation yield the total suspended sediment load during the observation period to be 10 × 10^6 kg. The sediment storage model assuming a reservoir beneath the glacier could bring the best estimate of variation in suspended sediment load. However, the multiple regression model gives a reasonable result and is also applicable for prediction.