After the relatively small MTT eruption, another period of magma accumulation into the shallow reservoir beneath Toba occurred. This time, however, the sub-volcanic system extended over 100 km parallel to the axis of Sumatra and was at least 30 km wide. The Batak Tumor would have inflated again, marking the epicenter for what was to come with regional uplift, earthquakes, and geothermal activity. The duration of such activity is unknown, but by 74,000 years ago, the system was rife for eruption. We may never know whether a major seismic event along the nearby Great Sumatran Fault triggered the eruption, or whether continued inflation of this enormous near-surface magma body reached a threshold whereby its roof could no longer be supported, but the results were the same: the greatest cataclysm the Earth has seen in the past 2 million years was now underway.