Color change of lake water at the active crater lake of Aso volcano, Yudamari, Japan: is it in response to change in water quality induced by volcanic activity?

Abstract

One feature of volcanic lakes influenced by subaqueous fumaroles existing at lake bottoms (called active crater lakes) is the remarkable color of their waters: turquoise or emerald green. The active crater lake named Yudamari at Mt. Nakadake of Aso volcano, Japan, takes on a milky pale blue-green. The particular blue component of the lake water color results from Rayleigh scattering of sunlight by very fine aqueous colloidal sulfur particles; the green component is attributable to absorption of sunlight by dissolved ferrous ions. An objective color observation conducted during 2000-2007 revealed that the lake water color changed from blue-green to solid green. The disappearance of the blue ingredient of the water color will result in diminution of aqueous colloidal sulfur from chemical analyses of lake waters sampled simultaneously. The aqueous sulfur is produced by the reaction of sulfur dioxide and hydrogen sulfide supplied from subaqueous fumaroles. However, its production efficiency decreases by domination of sulfur dioxide in the subaqueous fumarolic sulfur gas species with increasing subaqueous fumarolic temperature. The disappearance of blue ingredients from the blue-green color of the lake water may be attributed to activation of subaqueous fumarole activity.

Temporal variation in the chemical composition (HCl/SO2) of volcanic gas associated with the volcanic activity of Aso Volcano, Japan

“…Here, we compare the observed HCl/SO 2 ratio of the volcanic gas with the acidity and temperature of the water of the crater lake (Ohsawa et al, 2010) in April and August 2003, which is in Period A, and in March and July 2007, which is in Period B. Although the water in both periods has an extreme acidity (pH < 0.4), the water during Period A is characterized by a higher acidity and higher temperature compared with that in Period B (Ohsawa et al, 2010); this implies, following Rowe et al (1992), that more active HCl evaporation is expected during Period A than Period B. Since the observed HCl/SO 2 ratio is higher in Period A than that in Period B, the relation of the observed HCl/SO 2 ratio with the acidity and temperature of the water of the crater lake, agrees qualitatively with Rowe's hypothesis.…”

Mercury fluxes from volcanic and geothermal sources: an update

“…Aso volcano, in the central part of Kyushu Island (328 53 ′ 6.36 ′′ N, 1318 5 ′ 7.44 ′′ ), Japan is an active volcano with a c. 20 km diameter caldera that has some post-caldera central cones, including Mt Nakadake, where the current activity is mainly concentrated. The crater contains one of the hottest and most acidic volcanic lakes, with water temperature in the range 40-80 8C and acidity levels of pH 21 to +1 during calm periods (Ohsawa et al 2003(Ohsawa et al , 2010Terada & Sudo 2012). Low-temperature gases are emitted from the lake surface, and intense active high-temperature gas emissions (approximately 800 8C) are produced by fumaroles on the southern crater wall (Shinohara et al , 2013 …”

A photographic method for detailing the morphology of the floor of a dynamic crater lake: the El Chichón case (Chiapas, Mexico)

“…Most crater lakes are deep and fill basins or entire craters with steep or nearly vertical walls; lake surfaces mostly remain rather stable, while vertical variations can be extreme (e.g., the Poás, Irazú, Santa Ana, Aso volcanoes) Mora 2005;Miyabuchi and Terada 2009;Ohsawa et al 2010). Acoustic sounding systems along horizontal transects on lake surfaces have been applied to visualize the bottom profiles of crater lakes (Martini et al 1994;Takano et al 2004;Mazot 2005;Mazot and Solikhin 2008).…”