The USGS reported that seismic tremor from Anatahan slowly increased during 16-26 July. A diffuse sulfur-dioxide plume drifted W on 17 July. According to a Washington VAAC report a low-level plume possibly containing ash drifted 50 km NW on 26 July. The Volcanic Alert Level was raised to Advisory and the Aviation Color Code was raised to Yellow. According to another Washington VAAC report on 28 July, an ash plume rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted N. Seismic tremor continued to increase. A sulfur dioxide plume drifted NW. The Volcanic Alert Level was raised to Watch and the Aviation Color Code was raised to Orange. During 29-30 July, seismic tremor levels remained elevated, but possibly slightly decreased.
Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory – “Reports provided courtesy of the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program.”