Seismic activity accompanied the Plinian phase. Earthquakes that could be felt at Misenum, twenty-nine kilometers across the bay, suggest significant ground movement in the immediate vicinity of the volcano. The earthquakes contributed to structural damage and complicated the evacuation of those who were still in the city.
The surges that killed the majority of Pompeii’s remaining population occurred in the early morning hours of what we would describe as the second day of the eruption. Researchers studying the deposit record have identified at least six alternating phases of surge and fall during the Pelean phase. The surges that most affected Pompeii — designated surge 4 and surge 5 in the sequence — arrived within hours of each other. The deposits they left are clearly distinguishable in section.
The temperature of the surges, as estimated from the degree of thermal alteration of materials in the deposits, ranged from approximately 180 degrees Celsius in the lower, more dilute surges to 220–260 degrees Celsius in the denser, more concentrated ones. At these temperatures, the biological effect on the human body is effectively instantaneous — the heat causes cellular disruption faster than the nervous system can register it. The contorted postures preserved in the casts are not the postures of people in the act of dying; they are the postures of people whose muscular systems contracted in response to extreme heat after death, the cadaveric pugilistic attitude that forensic pathology recognizes as a heat-induced phenomenon.
This reconstruction matters for understanding the casts. The postures — which have been described as expressions of fear, of agony, of final human emotion — are primarily a record of physics acting on biology after the fact of death. The person in the House of the Golden Bracelet who held a child may have been holding that child before the surge arrived; the preservation of that posture may reflect their last conscious act. Or the posture may have been partially shaped by subsequent thermal effects on the muscular system. The distinction is not readily visible in the cast.