View article

4 increasing frequency and intensity, the ground vibrations called volcanic tremor, localized uplift of the surface, ground cracks, and anomalous gas emissions. Of all the possible hazards from a future volcanic eruption in the Yellowstone region, by far the least likely would be another explosive caldera-forming eruption of great volumes of rhyolitic ash. Abundant evidence indicates that hot magma continues to exist beneath Yellowstone, but it is uncertain how much of it remains liquid, how well the liquid is interconnected, and thus how much remains eruptible. Any eruption of sufficient volume to form a new caldera probably would occur only from within the present Yellowstone caldera, and the history of postcaldera rhyolitic eruptions strongly suggests that the subcaldera magma chamber is now a largely crystallized mush. The probability of another major caldera-forming Yellowstone eruption, in the absence of strong premonitory indications of major magmatic intrusion and degassing beneath a large area of the caldera, can be considered to be below the threshold of useful calculation.