© 2018, The Author(s). This paper presents data from an online survey carried out in Mexico from 2012 to 2014. The survey focussed on the risk to Mexico City from Popocatépetl, an active volcano 60 km from the city. During the time period, volcanic activity was variable, and the alert level changed accordingly. The survey showed that people surveyed at the higher alert level were generally more concerned about the volcano. Since these people were measured separately from those who responded at the lower alert level and yet self-reported on the same scale as more concerned, this provides a useful indicator that the raised alert level may be associated with higher risk perception, and that alert level systems act as boundary objects in the translation of scientific information. In general, trust in various groups was most strongly explained by the perceived knowledge of the groups, followed by their perceived motivation (whether or not they are viewed as working in society’s interest), with accuracy a tertiary concern. Some respondents were anxious about false alarms—these people also tended to be concerned about scientific accuracy while those who favoured precaution tended to be more trusting. The perceived effectiveness of warning and evacuation plans was also a significant predictor for trust in official groups. In general, the results suggest that there are important links between trust, warning plans and the perceived motivation of particular groups as well as between trust and perceived knowledge.