The issue is well summarised by Miller in this recent note in PNAS. "Recent workers aiming to assess histories of eruptible magma and consider consequences for eruption hazards tend to fall into two camps, as described in Barboni et al. (1). In the first camp are the “cold storage” advocates, who suggest that magmatic materials are crystal-rich and ineruptible, perhaps even subsolidus, throughout most of their history, but that they become briefly eruptible as a result of thermal rejuvenation. . The second camp is composed of those who favor “warm storage” and estimate that during much and perhaps most of >105 y magma system histories eruptible magma is stored beneath volcanoes." . It remains to be seen whether the cold storage or warm storage view has greater validity; perhaps more likely, different systems have different storage styles, or the reality of typical magma system behavior incorporates elements of both." In the same issue of PNAS the case for warm storage is made by Barboni et al who say " The increasingly popular notion that steady-state magma chambers are highly crystallized, and thus only capable of erupting during brief (<1 ka) reheatings, implies that melt detection beneath volcanoes warns of imminent eruption.....we show that arc magmas may generally be stored warm (are able to erupt for >100 ka). Thus geophysical detection of melt beneath volcanoes represents the normal state of magma storage and holds little potential as an indicator of volcanic hazard." If cold storage were the only, or the predominant mechanism, then detection of melt beneath a dormant volcano provides advance warning of potential eruption. One would expect that as our detectors become more sensitive, our software more sophisticated, our grasp of the mechanisms acting within magma chambers more refined, that it will be possible to predict eruptions with a high degree of accuracy. At present we are far removed from this.