For many years, most scientists implicitly assumed that crustal-scale processes (eg., volcanism) and surface processes (eg., precipitation) operate at such different spatial and temporal scales that the latter would be unlikely to affect the former. However, data from high-precision, long-term, and continuous sensor networks are beginning to show that, instead, processes operating deep within the Earth are sensitive to events happening at or near its surface. For example, uplift in the Sierra Nevada detected by a network of GNSS stations (it's the same idea as GPS) was found to be caused by seasonal changes in groundwater levels and a long-term drought (Amos et al., 2014, Nature ). In a paper published in Geophysical Research Letters , George Hilley and his colleagues analyzed data from the GNSS network and a CO2 (carbon dioxide) sensor near the Mammoth Mountain ski area along the eastern slope of the southern Sierra Nevada. The goal of the study was to understand the processes co