Lava boils seawater completely dry

The lava ocean entry at East Lae`apuki, on the southern shoreline of Kilauea Volcano, has been active for 15 months. Lava flows rapidly from Pu`u `O`o into the sea, hardly cooling at all, owing to the thermal insulation provided by the lava tube it travels through. Dense, white steam plumes mark the closely spaced lava entry points. Kilauea Volcano is well known for its entries of lava into the ocean. It is not the only place in the world where lava flows into the sea, but even so, lava entries of this type are scarce.

Although basalt is the most abundant magma type, most of it erupts beneath the sea, at mid-ocean ridges. Only a small fraction of basaltic volcanoes are on land and are close to the shoreline.

Ocean island volcanoes are in this small category. These are volcanic islands generated by the movement of the Earth’s crust over a stationary mantle plume, which causes magma to punch through the crust at intervals. This process, over long periods of geological time, forms a chain of volcanic islands.

An example of an Ocean Island Chain extends from India to Reunion Island, in the Indian Ocean. Part of Reunion Island is made up of the volcano Piton de la Fournaise, which is currently active. It erupts a similar kind of basalt lava to Kilauea and Mauna Loa volcanoes. Lava enters the ocean occasionally—the last time was in August 2004.

At present, an eruption of Montagu Island in the South Atlantic (which began in September 2005) is pouring lava into the ocean. So far, an area the size of 30 football fields has been tacked on to the shoreline. At Stromboli, lava flows entered the sea during 2003 and sent up billowing white steam clouds. Flocks of seabirds gathered to eat the boiled fish, which floated up to the ocean’s surface near the lava entry.

New research sheds light on the thermal and chemical processes occurring at the lava entry. When lava has contact with seawater, the supplied heat is enough to boil the seawater completely dry. This is different than boiling seawater to salty liquid brine. How do we know this?

Measurements of gases in the steam plume generated when lava enters the sea show that steam and hydrogen chloride gas are present in proportions that can result only from the thermal breakdown of the magnesium salts in seawater and not from the sodium salts as was previously thought. This is surprising, as seawater contains much more sodium than it does magnesium.

The sequence of precipitation from evaporating seawater is well known and starts with calcium carbonate (chalk) when around 50% of the seawater is evaporated, calcium sulfate (gypsum) at around 80%, sodium chloride (table salt) at 90%, and magnesium salts at 98%. In other words, seawater must be boiled almost completely dry before magnesium salts form. The salts then react with steam to form hydrogen chloride gas. These new findings contribute to our growing understanding of the interactions between the solid Earth, our oceans, and own atmosphere.

Activity Update

Activity at the summit of Kilauea Volcano has remained at moderate levels this past week. Frequent earthquakes continue beneath three areas – the upper east rift zone of Kilauea from the summit caldera to Pauahi Crater, the Namakani Paio campground/Kipauka Puaulu area, and the south summit caldera. Inflation of the summit caldera continues at the accelerated rate started on January 12, 2006.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with occasional surface flows breaking out of the tube. In the past week, surface flows were active near the 2,300-ft elevation and on the coastal plain below Paliuli, 0.75 km (0.5 mi) inland of the coast at Kamoamoa and 5.5 km (3.4 mi) from the end of Chain of Craters Road.

As of March 9, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 900 m long by 200 m wide. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were again eight earthquakes beneath Hawai`i Island reported felt within the past week. Four of them occurred in two pairs, each pair no more than 7 minutes apart. All were located in the same Namakani Paio/Kipuka Puaulu area 5 to 9 km (3 to 5 miles) northwest of Kilauea summit at depths between 3 and 7 km (2 to 4 miles). Magnitude-2.7 and -3.9 earthquakes occurred on Thursday, March 2, at 3:38 and 3:45 p.m. Magnitude-2.4 and -2.6 earthquakes occurred at 12:04 and 3:35 p.m. on Friday, March 3. Magnitudes-3.8 and -2.9 earthquakes occurred at 3:41 and 3:45 p.m. on Saturday, March 4. Magnitude-3.9 and -3.1 earthquakes occurred at 5:56 and 7:38 a.m. on Monday, March 6.

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano’s summit. Inflation continues, but at a rate that has slowed since early October 2005.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by HawaiiNews.com with permission.