(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

The Island of Hawaii, a composite of five volcanoes, has a surface area almost twice as large as the other main Hawaiian Islands combined. Such a size provides some level of security for the island’s residents during volcanic eruptions because, in general, it takes time for lava flows to reach inhabited areas. This is especially true on Kilauea, which has a fairly modest long-term eruption rate of about 3 to 6 cubic yards of lava per second.

When lava from the most recent phase of the eruption began flowing southward in November 2007, it took three months for it to finally reach populated areas along the coast. It took even longer—about four months—for lava flows from the Kupaianaha vent to reach an equivalent distance in 1986. In both examples, there was time for people to move themselves, their belongings, and, in some instances, their homes, before the lava arrived.

Such circumstances, however, are not always the case, and two relatively recent examples are worth mentioning. One took place last summer (2008) on the tiny Aleutian volcanic island of Kasatochi, about 1,100 miles southwest of Anchorage, Alaska. Long considered dormant, Kasatochi Volcano began to stir at the beginning of August. The small earthquakes that started to occur were not detected by seismometers on nearby islands, but were felt by the two U.S. Fish and Wildlife biologists stationed on the island for the summer.

A few days later, on Aug. 6, after the tremors had continued to increase in frequency and magnitude, and finally became detectable by the sparse Aleutian seismic network, an evacuation plan was initiated. To the discomfort of all involved—especially the two biologists—the nearest Coast Guard rescue option was at least 24 hours away. Luckily, a fisherman from nearby Adak Island, about 50 miles away, offered to sail to Kasatochi the following morning.

Anxieties mounted as dawn broke with fog and heavy surf on Aug. 7. Earthquake activity had continued to ramp up overnight, and poor weather raised questions of whether the small fishing vessel would reach the island. Fortunately, the boat arrived, as promised, and the biologists evacuated. Just how dire were the circumstances? As the fishing boat made the difficult return to Adak Island, Kasatochi erupted, sending ash to a height of 35,000 feet and burying the entire island beneath pyroclastic flows.

Though the Kasatochi rescue was a narrow escape, it was still far better than no escape at all—the predicament of Yemeni soldiers on the tiny volcanic island of Jabal al-Tair, off the coast of Yemen in the Red Sea, in September 2007. In that event, the volcano, which is about the size of Kilauea’s summit caldera, erupted with little warning, causing a portion of the volcano to collapse into the sea. Much of the rest of the island was quickly buried beneath lava flows.

Most of the soldiers stationed at the small Yemeni naval base on the island were evacuated, but some were forced to flee into the water to escape being overtaken by lava. For them, the struggle then became a fight to avoid drowning or being boiled alive. After hours of treading water, the scattered survivors of this small group—and the bodies of their unlucky comrades—were plucked from the water by search vessels. In total, nine soldiers were killed and dozens of others were injured.

With these two incidents in mind, one might ask if similar close calls or tragedies could occur on Hawaii Island. After all, the lower portion of Kilauea’s east rift zone cuts through the middle of a well-populated part of Puna, and an eruption there could potentially cut off evacuation routes. Likewise, on Mauna Loa’s southwest rift zone, the steep slopes and potential for rapidly moving flows could also cut off evacuation routes.

While such scenarios are possible, with dozens of monitoring instruments dotting the volcanoes on Hawai`i, precursory activity to eruptions should be detected at least a few hours in advance, forewarning those in harm’s way. If you are aware of volcanic hazards in your area and take heed of warnings, then sleeping with a surf board next to your bed won’t be necessary.