During a typical explosive eruption of a Mono-Inyo vent, tephra (volcanic ash and larger rock fragments) may accumulate near the vent to a thickness of 10 m. Areas downwind of an explosive eruption could be covered with a layer of volcanic ash and pumice more than 20 cm (8 in) thick at a distance of 35 km (22 mi) and 5 cm (2 in.) at 85 km (53 mi).

It is not possible now to predict wind direction or directions that will exist at the time of a future explosive eruption. However, records suggest that on an annual basis winds in the area blow toward an east or northeasterly sector more than 50 percent of the time, and toward some easterly direction more than 80 percent of the time. In general, the grain size and thickness of ash accumulations gradually decrease with increasing distance from a vent.

Areas as far as 15 km (10 mi) from an explosive eruption could be swept by hot, fast-moving pyroclastic flows and surges. This zone is based on the distance that pyroclastic flows are known to have traveled in the past few thousand years. The actual areas covered by pyroclastic flows or surges during a future explosive eruption depends primarily on the location of the vent(s), the surrounding topography, and volume of magma erupted.

Pyroclastic flows generated from vents on Mammoth Mountain could travel farther than 15 km (10 mi) because of the extra momentum that would be gained as the flows descend hundreds of meters down Mammoth's steep flanks and move across low-lying areas.

Molten rock moving across the ground as a lava flow seldom threatens human life directly because its slow rate of advance allows people to move out of the way. Once lava erupts from a vent, its potential pathway is predictable because lava moves down hill according to the local topography.

Future lava flows in the Long Valley area will be either relatively fluid (basalt lava) or viscous (dacite or rhyolite lava). Basalt lava typically forms thin flows that may reach distances of more than 50 km (30 mi) from their vent. Dacite and rhyolite lavas typically produce short, thick flows that seldom move as far as 5 km (3 mi) from the vent. These short flows often build mound-shaped features called lava domes.

The principal hazard associated with formation of a dome results from pyroclastic flows, and from rock fragments thrown out by explosions, which may reach 5 to 10 km from the dome). The sides of a growing lava dome are steep and unstable, and sometimes collapse to form pyroclastic flows that can move outward at least 5 km from the dome. Pyroclastic flows may travel progressively farther as a dome grows higher or if the dome is located well above surrounding areas (for example, on Mammoth Mountain, which was built by a series of overlapping lava domes).

Explosive eruptions inject large amounts of volcanic ash and corrosive gases high into the atmosphere, especially into cruising altitudes used by commercial jet airplanes. Volcanic eruption clouds may drift for hundreds to thousands of kilometers from an erupting volcano, and can contaminate heavily used aeronautical routes over wide areas. Volcanic ash can damage aircraft flying surfaces and electronics, and cause engine failure. Eruption clouds also may cause flights to be diverted, delayed, or canceled.

Since winds above the Long Valley area blow toward an easterly direction more than 80 percent of the time, air routes east of the volcano are likely to be contaminated with volcanic ash during a future eruption. For example, air routes within a few hundred miles east of Long Valley that accommodate jets either approaching and departing San Francisco or flying in a north-south direction toward or away from Las Vegas, Nevada.