|Hazard zones for lava flows on Kilauea. The flows erupted since 1800 are shown in gray and dated. Twenty-eight percent of the area encompassed by Zones 1 and 2 on the east half of the volcano has been covered by lava since 1955. The major housing subdivisions on the slopes of the volcano are shown in green.|
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. In historical time, all of Kilauea's eruptions have occurred either in or near its summit caldera, or along the east or southwest rift zones. For the foreseeable future, we can assume that active vents will be limited to these areas.
Since 1955, 28 percent of the area encompassing the east rift zone and the slope south of the rift zone has been covered by lava flows. The latest eruption of the east rift zone began in 1983 and continues as of 1996. The southwest rift zone is less active, with five eruptions in the past 200 years; the latest was in 1974. The most recent summit eruption occurred in 1982.
From the time of the first written accounts in the early 1800's and through the first decades of this century, Kilauea erupted almost continuously at its summit caldera. In 1924, the summit caldera's active lava lake in Halemaumau crater abruptly drained away, and ground water beneath the caldera apparently came into contact with the hot rocks surrounding the magma conduit, causing a series of steam explosions that threw out large blocks of dense lava along with ash. Sporadic eruptions continued at Halemaumau until 1934, when all activity ceased for 18 years. In 1952, Kilauea reawoke with a 4-month eruption in Halemaumau. Since then, eruptive activity has occurred mainly on the volcano's two rift zones, particularly the east rift zone. From 1969 to 1974, Kilauea erupted at the Mauna Ulu vent on the upper east rift zone. The Mauna Ulu eruption was the most voluminous rift eruption in over a century but has been surpassed in both volume and duration by the recent eruption at the Pu'u 'O'o and Kupaianaha vents.
The hazard map for Kilauea shows the relative degree of hazard from lava flows for different areas of the volcano. Zone 1 is the most hazardous; it consists of the summit area and rift zones because Kilauea's frequent eruptions originate in these areas.
|Steam rises from the Kalapana shoreline where lava flows from Kupaianaha entered the ocean in 1987. The Pu'u 'O'o cone (P) marks the east rift zone; Kupaianaha (K) is the low mound on the center skyline. All of the area from the rift zone to the ocean is in Zone 2. The streets of Royal Gardens are visible on the slope at center.|
Zone 3 includes the areas north of the upper east rift zone and both north and south of the southwest rift zone. Less than 5 percent of the area in Zone 3 has been covered with lava in historical time, but more than 75 percent has been covered in the last 750 years.
Zone 2 includes the areas that are adjacent to, and downslope from, the east rift zone. The entire area south of the east rift zone lies in this zone. Lava flows are most likely to travel in this direction because the ground slopes downhill from the rift zone to the ocean. The area north of the lower east rift zone, which includes Pahoa, is also in Zone 2. Here the land slopes away to the north as well as the south, and flows can advance in either direction.
No area on Kilauea is ranked Zone 4, but the area south of Kilauea's
summit is classed as Zone 5. This flank of Kilauea is currently protected from
lava flows by the location of the summit caldera and by north-facing fault scarps
(steep slopes or cliffs that form as the result of movement along faults).
Because of those topographic barriers, almost none of this area has been affected
by lava flows during historical time, although nearly half of it has been covered
within the last 750 years.