Case
Study

Introduction

Where: Mount Kilauea, Hawaii, U.S.A.

When: 1983 - 2000

Type of volcano: Shield volcano

Type of eruption: Gentle lava flows - now in its eighteenth year of continuous eruption

Deaths: No deaths but much damage

Kilauea is Hawaii's youngest volcano and one of the world's most active. Over 90 percent of Kilauea's surface is covered by lava less than 1,100 years old. All of Kilauea's eruptions have occurred either in or near its summit crater, or along the east or southwest rift zones which are long cracks in the slopes of the volcano. When Kilauea began to form is not known, but estimates vary from 300,000 to 600,000 years ago. The volcano has been active ever since, with no prolonged periods of inactivity known. Most eruptions are relatively gentle, sending lava flows downslope from fountains a few metres to a few hundred metres high. Over and over again these eruptions occur, gradually building up the volcano and giving it a gentle, shield-like form. On rare occasions, powerful explosions spread ejecta across the landscape. Such explosions can be lethal, such as the one in 1790 that killed scores of people in a war party near the summit of Kilauea.

Beginning in 1983, a series of short-lived lava fountains built a massive cinder-and-spatter cone known as Puu Oo at the summit. In 1986, the eruption migrated 3 km down the east rift zone to build a broad shield called Kupaianaha, which fed lava to the coast for the next 5.5 years. When the main activity shifted back to Puu Oo in 1992, a series of eruptions caused the summit cone to collapse and form a large caldera.

The high lava fountains from Puu Oo produced mainly aa flows, the more viscous (sticky) of the two types of Hawaiian lava. Aa flows from Puu Oo were typically 3-5 m. thick and advanced at speeds of 50-500 m./hr., picking up speed and narrowing on steep slopes. Because each eruption was short-lived, none of these flows reached the ocean or the coastal highway. The flows posed an immediate threat, however, to the sparsely populated Royal Gardens settlement, located 6 km. southeast of the vent. Aa flows reached the settlement in as little as 13 hours on several occasions. They destroyed 16 houses in 1983 and 1984.

In 1986 the eruption shifted to a new vent, Kupaianaha, 3 km. northeast of Puu Oo. This marked the end of the high lava fountains and the beginning of five-and-a-half years of nearly continuous, quiet outpourings. A lava pond formed over the new vent, and its frequent overflows built a broad, low shield that reached its maximum height of 55 m. in less than a year. Eventually, the main channel exiting from the pond gradually developed a roof as crust at the sides of the channel extended across the lava stream, forming the beginning of a lava tube. Lava tubes insulate rivers of lava from heat loss, producing pahoehoe, a type of lava more fluid than aa.

Late in November 1986, flows from Kupaianaha reached the ocean, closing the coastal highway. A few weeks later, the lava took a more easterly course and destroyed 14 homes on the northwest edge of Kalapana in a single day. Over the next three years, lava destroyed homes on either side of the ever-widening flow field. From mid-1987 through 1989, most of the lava erupted from Kupaianaha flowed directly to the sea. New land was added as lava built a series of benches seaward. In the spring of 1989 the lava flows changed direction, overrunning the Wahaula Visitor Centre and nearby houses in Hawaii Volcanoes National Park.