May 2, 1997
A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.
The Mauna Ulu eruption 1969-1974
The Mauna Ulu eruption on Kilauea's east rift zone began 28 years
ago this month, on May 24, 1969. For the next 2.5 years eruption was
almost continuous and often spectacular. The eruption was the longest
and largest on the rift zone in post-contact time until surpassed by
the Pu`u `O`o eruption. After a 3.5-month pause (October 15,
1971-February 3, 1972), Mauna Ulu resumed erupting and continued to
July 1974.
Mauna Ulu formed between `Alo`i and `Alae Craters, popular stops
along the old Chain of Craters Road. These craters are now only
memories, for lava filled both of them during the eruption. The present
road, rerouted around the Mauna Ulu area, bends away from the rift zone
1.3 km (0.8 mi) west of `Alo`i and intersects the old road at the top
of Holei Pali.
Twelve fountaining episodes highlighted the first six months of the
Mauna Ulu eruption. Six produced fountains 300 m (1,000 ft) or more
high. One, on September 6, towered to 540 m (1,770 ft), a height
surpassed only once in this century (580 m (1,900 ft) during the 1959
Kilauea Iki eruption). The fountains were readily seen and heard from
Volcano, and the Uwekahuna overlook at the U.S. Geological Survey's
Hawaiian Volcano Observatory (now the Jaggar Museum) was often crowded
with spectators enjoying the show. A privileged few watched some of the
fountains from the top of nearby Pu`u Huluhulu, where the heat was
nearly unbearable.
The fountains fed fast-moving lava flows that traveled as far as the
coast, 12 km (7 mi) away. In the wee hours of June 26, hundreds of
visitors along the coastal road in the Kealakomo ahupua`a were
entranced by the majestic spectacle of lava pouring in broad surges
down 220-m (700-ft) high Holei Pali.
Between periods of fountaining, lava splashed and circulated in the
vent of Mauna Ulu, sometimes forming low fountains, sometimes quietly
upwelling and overflowing the vent. Similar activity continued for
months after the last high fountain on December 30, 1969. Overflows
built the Mauna Ulu shield until mid-1970 and again added to it in
1972-74. By the time it stopped growing, Mauna Ulu stood 121 m (400 ft)
above its pre-eruption base. Its summit crater, at times as deep as 200
m, had shallowed to about 30 m (100 ft) when the eruption ended.
Lava tubes gradually developed as flows moved away from Mauna Ulu
during periods of continuous weak activity. The tubes frequently
carried lava into the ocean in 1970-74, from west of `Apua Point to
east of Ka`ena Point, burying the road and archeological sites at
Kealakomo.
`Alae was a large crater southeast of Mauna Ulu, 440 m (1,440 ft) in
diameter and 165 m (540 ft) deep. It filled grudgingly. By midnight on
August 3-4, 1969, flows from Mauna Ulu had almost filled `Alae to
within 10 m (30 ft) of its rim. Four hours later, hundreds of
earthquakes accompanied the opening of a wide crack across the crater
floor, and most of the liquid lava in the lake drained away. In 30
extraordinary minutes, lake level dropped 80 m (260 ft) as 10 million
cubic meters (13 million cubic yards) poured underground. The crack,
locally 10 m (30 ft) wide at the surface, transported the lava 7.5 km
(4.5 mi) downrift, where some eventually erupted later in the day.
Fountain-fed flows in September and October cascaded as red-hot
Niagaras into `Alae, completely filling it on October 20, 1969. By
1974, more flows had built a shield nearly 90 m (295 ft) high over the
buried crater; perched ponds on the shield can be seen makai of the
Napau trail.
The writer witnessed many of these remarkable events. The memories
are indelible.
Eruption Update: May 2
Kilauea's east rift zone eruptive activity is limited to a sustained
lava pond within the Pu`u `O`o Crater and to two vents on the west and
south sides of Pu`u `O`o. The western vent has built a 15-meter-high
spatter cone and occasionally sends flows to the west and southwest.
Lava from the southern vent flows into a perched pond which feeds `a`a
flows to the southeast. The recent media blitz on the eruption was due
to the availability of excellent video footage and not because of any
change in the eruption.
Earthquakes
There were no earthquakes reported felt during the past week.
The URL of this page is
http://hvo.wr.usgs.gov/
Contact:
webmaster@wwwhvo.wr.usgs.gov
Updated :
|