July 19, 1996

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Steaming Vents at Kilauea: Stay on the Trails!

On Wednesday, July 17, a 10-year-old boy slipped into a large crack in the Sulphur Banks - Steaming Flats area of Hawaii Volcanoes National Park. Unfortunately, the crack was also a vent for steam, which scalded the young visitor and caused second-degree burns.

There is an abundance of cracks in the summit and rift zone regions of Kilauea, and these cracks are a geologic hazard that can be mitigated only by avoidance. The large number of cracks between the National Park Visitor Center and the Kilauea Military Camp is part of the caldera fault system.

Kilauea caldera was formed by multiple collapses of the summit region. Each collapse produced a set of ring fractures reflecting the location, depth and size of the magma body that was being drained. The caldera boundary faults often serve as passageways to the Earth's surface for the volatile gases within the magma body. The solfataras that form the Sulphur Banks are an example of a caldera ring fault degassing a magma body.

The more than 80 steam vents in the Steaming Flats allow the release of water heated by a magmatic body. The temperature in these cracks is about 145 degrees Fahrenheit, and the visibility of the steam is largely dependent upon the humidity and temperature of the surrounding air. Analyses of the water from the condensed steam confirm the presence of tritium, a radioactive form of hydrogen that was introduced to the atmosphere by nuclear explosions. The presence of tritium indicates that the source of the water is meteoric (rain or fog), rather than magmatic.

Long, linear cracks are common in the rift zones, and they represent the surface manifestations of dikes that intrude the rift zone. As these planar magmatic bodies move into the rift zone, a pair of parallel ground cracks form along the direction of movement. If the dike reaches the Earth's surface, it becomes the familiar line of fire, the eruptive fissure at the onset of an eruption.

The danger of ground cracks is that they are often hidden by vegetation, mainly uluhe, the false staghorn fern. The National Park Service urges all visitors to stay on the marked trails. The recent series of accidents in the Park was the result of people's wandering off the trails or straying beyond safe areas.

Kilauea Eruption Update

The Kilauea eruption continues unabated, and lava enters the ocean in the Lae`apuki region. Another large bench collapse involving several acres occurred on July 12. The collapse was accompanied by violent explosions as the seawater entered the lava tube system.

Earthquakes

Two earthquakes were felt on the morning of July 18. Both temblors were located 7 miles northwest of the summit of Mauna Kea at a depth of about 17 miles. The first quake at 7:39 in the morning was felt island-wide and had a magnitude of 4.4 on the Richter scale. A small aftershock 9 minutes later was felt in Pa`auilo and Keahole. There were no reports of damage from either event.

Shortly before 10:00 on the night of July 16, the U.S. Geological Survey's Hawaiian Volcano Observatory seismic network started to record a swarm of earthquakes from Lo`ihi Volcano. Lo`ihi is a submarine volcano located 20 miles off the coast of Ka`u. The largest of the swarm had a magnitude of 4.2 and occurred at 6:53 on the morning of July 17. The activity continues as we write this article on Friday, July 19.