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

It may surprise some readers that the Puu Oo eruption, now halfway through its 28th year of almost continuous activity, is not the longest-running eruption on Earth. A number of other ongoing eruptions started before 1983, when Puu Oo began to form, according to the database painstakingly compiled by the Smithsonian’s Global Volcanism Program (http://www.volcano.si.edu/world/).

The leader is Stromboli, the northeasternmost of the Aeolian Islands north of Sicily. It is often called the “Lighthouse of the Mediterranean,” because it has been erupting almost continuously for more than a millennium and served as a beacon for ancient mariners before the birth of Christ. Its eruptive activity consists of generally mild ejection of spatter, with infrequent lava flows.

Mount Erebus, a huge volcano 3,794 m (12,447 feet) high overlooking the McMurdo research station on Ross Island in Antarctica, was first sighted in eruption by Captain James Ross in 1841.

Its continuous eruption, in a lava lake at the volcano’s summit, has been documented since 1972 but, according to the Smithsonian, has probably been occurring for much of the volcano’s recent history.

Perhaps the least known of the long-lasting eruptions is that at Erta Ale, a basaltic shield volcano in Ethiopia. Erta Ale is 50 km (30 miles) wide and 613 m (2,011 feet) high, rising from below sea level in the Danikil Depression.

One of two lava lakes has been active in the summit caldera since at least 1967 and possibly since 1906. Lava also erupts infrequently from fissures outside the caldera.

Several volcanoes in Central America have been erupting more or less continuously for a few decades. Santa Maria (Guatamela) is producing the huge lava dome, Santiaguito, which began growing in 1922. Arenal (Costa Rica) has been erupting since 1968, with mild explosive eruptions and lava flows. See the Smithsonian’s database for more examples of long-lasting, ongoing eruptions.

Although Kilauea’s eruption at Puu Oo may not top the list in terms of longevity, several of its characteristics stand out from those of its older rivals.

Perhaps the most striking distinguishing feature is that all of the other ongoing eruptions are taking place at or very near the summit area of each volcano. This makes sense, since magma rises from great depth beneath the summit of a volcano; it is relatively easy to maintain an eruption there, as long as the supply of magma remains unbroken.

Puu Oo, however, is 20 km (12 miles) from Kilauea’s summit and is fed by magma moving from the summit reservoir into the east rift zone. For some unknown reason, it has been easier for Kilauea to erupt at this distant vent than in the summit caldera itself. The combination of duration and distance from the summit makes Puu Oo unique among today’s ongoing eruptions.

Another important distinction is that the volume of lava erupted from the Puu Oo-Kupaianaha vent area far surpasses that from any of the other volcanoes. In fact, the total volume of lava erupted by all the other ongoing eruptions in the past 100 years, excepting the Santiaguito dome, probably wouldn’t exceed that which extruded from Puu Oo. This reflects the high rate of magma supply to Kilauea. The volume erupted at Santiaguito since 1922 is large, about 1.5 cubic kilometers (0.4 cubic miles), but the volume erupted at Puu Oo since 1983 is more than twice that amount.

In human terms, the Puu Oo eruption has probably been the most destructive of all the ongoing eruptions, at least regarding the number of houses destroyed and highway miles covered.

The other continuously active volcanoes are all in areas of low population density, and most are far from major roadways. All eruptions that cover cultivated land hurt the population, however, and a farmer whose crops are destroyed is injured no matter where the eruption takes place.

In the end, it is not statistics or records that are important. Each ongoing eruption has its own facts, neither better nor worse than those of the other eruptions.

Readers should pay little attention to comparison for comparison’s sake and, instead, look into each eruption in more depth to acquire a fuller sense of what makes long eruptions work. The Smithsonian database is the best place to start.