Scientists say that pressure is building up under the Crater Lake on Mt Ruapehu, increasing the likelihood of an eruption in the coming weeks. GNS Science said recent measurements taken on the volcano over the last few weeks indicated that eruptions were more likely "over the next weeks to months". Pressure build-up was thought to have caused the 2007 eruption and a smaller eruption in 2006. The Aviation Colour Code has increased from green to yellow as a warning for those flying over the region, but the Volcanic Alert Level remained at level 1. GNS Science believed the temperature a few hundred meters beneath the crater was about 800 degrees Celsius but the lake itself was only 20degC. GNS constantly monitored Ruapehu and had discovered over the last few weeks that the chemistry and gases within the Crater Lake were changing. The criteria for the aviation code and alert levels were not the same and the heightened temperature of the lake meant GNS was required to change the aviation code, Scott said. Alert level 1 indicated that the volcano was in a state of unrest, while an actual eruption was needed to increase it to level 2. ubAlert