A major explosive volcanic eruption in Chile has occurred at volcan Calbuco. This volcano has been quiet for over 40 years, and showed no sign that it was about to erupt until just a few hours beforehand. This eruption created a spectacular plume, which sent ash and gases high into the atmosphere, disrupting air transport and causing misery on the ground. In the three days after the eruption, volcanic ash fell across a wide area of central South America, across areas that include ancient native forests; cities, towns and villages; and farms, both on land and at sea. We plan to carry out field work across areas of Chile and Argentina where ash fell, working with local scientists to measure how much ash fell out during the eruption; and to work out what the effects of the eruption are both in the weeks after the eruption, and in the longer term. Although this is a major eruption, much of the deposits will soon become buried within the soil; blown away by winds, or washed away by rain, so we will need to work quickly to find the ash where it fell. Since ash fell out across an area where many millions of people live, we should be able to work out how much the deposits have changed in the days and weeks since eruption, by locating photographs posted across social media at the time. One of the things that we hope to learn from this eruption is to work out how to help people cope better when ash falls out across their cities and farms, and to use this information to help plan for future events.