Basaltic lava flows and small, associated, local ash falls, are the most common volcanic activity at Lassen volcanic center.
These eruptions typically last a few months to a year, but may continue for several years. They can cover more than a square mile with lava flows, but because these eruptions are relatively nonviolent, they rarely impact the human population.
A greater hazard is associated with more silicic lava flows. Past dacite eruptions have formed lava domes, which are inherently unstable and can collapse to produce block and ash flows that travel several miles.