Use of a weather buoy to derive improved heat and mass balance parameters for Ruapehu Crater Lake

Heat and mass balance calculations are important for monitoring volcanoes with heated crater lakes, but for these lakes the critical process of evaporation can be substantially affected by the lake's influence on the air mass above it. Measurements in 2010 using a weather station on a buoy floating in Ruapehu Crater Lake enabled us to derive a relation between wind velocity above the lake and that measured at nearby weather stations, as well as providing direct evidence of the effect of the warm lake on the air above it. This supported the use of evaporation equations that allowed for the changing air conditions as incoming air became warmer and wetter from interaction with the lake, so decreasing the overall evaporation rate.Heat and mass balance calculations using these parameters and equations during the period 2003 to early 2007, as Crater Lake filled before it overflowed, confirm the previously observed high ratio of total heat flow to steam volume.

► We recorded the atmospheric conditions above the warm Ruapehu Crater Lake. ► The air above the lake was hotter and wetter than ambient. ► Evaporation from warm lakes is affected by the changing air properties.