Figure 5. Temporal trends in volcanic activity can be represented by the cumulative number of volcanic vents and cumulative volume of volcanic events through time. Here, volume is represented as area covered by lava flows, which is more easily and accurately determined from maps than lava flow volumes. The cumulative area covered by lavas was remarkably steady in the Springerville volcanic field (see Figure 1) between 1.75 and 0.75 Ma. Such steady-state volume-time relationships have been observed in several volcanic fields. In contrast, the recurrence rate of volcanic events waxes then wanes during this period.