Both the Long Valley Caldera and Yellowstone Caldera are considered resurgent calderas. Changes in the caldera floor indicate magma movement at various depths beneath both calderas. The caldera floors have been slowly doming upward since the cataclysmic explosions occurred eons ago. The effects of volcanoes can be divided into primary and secondary effects, which could also be called primary and secondary causes for human concern. Primary effects are produced directly by the volcanic activity.
Secondary effects are the result of primary effects.
Disruption of normal human activity, such as sanitation and farming leads to famine and disease. Gas content and eruptive temperature are essential factors in the lava flow's behavior. This produces A'a, which has a blocky texture and a jagged surface. Most lava flows are slow enough that they are seldom a threat to human life. Such flows generally follow a predictable course.