From April 9 to July 5, the alert level on Taal Volcano was raised from 1 to 2 because of the increased seismicity of Volcano Island. Frequency peaked at about 115 tremors on May 30 with a maximum intensity of IV, accompanied by rumbling sounds. Magma was intruding towards the surface, as indicated by continuing high rates of CO2 emissions in the Main Crater Lake and sustained seismic activity. Field measurements on May 24 showed that lake temperatures had increased slightly, pH values were slightly more acidic, and water levels were higher. A ground deformation survey conducted around Volcano Island from April 26 to May 3 showed that the volcano edifice had inflated slightly relative to the April 5–11 survey.