Geologist examines spatter and ash deposits within Hawai‘i Volcanoes National Park along Kīlauea’s southwest rift zone. New understanding of the age of the ash deposits, based on years of careful research, has prompted an important revision of the ages of these surface lava flows. USGS photograph by Tim Orr, November 6, 2015.
(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
Sometimes the days go by and you don’t seem to accomplish much. E-mails, phone calls, paper work, futzing around just aren’t getting you anywhere. Faced with frusUtration, it’s good to stand back, take a deep breath, and examine what has been learned during decades of study of Hawaiian volcanoes. From such perspective, astounding progress has been made, and we at the Hawaiian Volcano Observatory have been privileged to be part of the story.
Unlike sausage making, the scientific learning process is open to observation, warts and all. Blunders, some rather embarrassing, will be caught, even if made by luminaries. For example, Thomas Jaggar, founder of the Hawaiian Volcano Observatory, once thought that KÄ«lauea was older than Mauna Loa, a conclusion quite opposite what we know today.
Generally, though, it is not blunders but small errors that are corrected. Even more often, new data or changes in interpretation drive the process forward. Progress is incremental, sometimes two steps forward and one step back or, momentarily, even the reverse. Grand breakthroughs are unusual, plate tectonics being an example.
With that said, where do we stand today with big-picture knowledge of KÄ«lauea and Mauna Loa acquired in the past few decades?
Hawaiian volcanoes seem to remain active for several hundred thousand, perhaps a million, years. Mauna Loa is well into its life span and will, eventually, be replaced by LÅÊ»ihi, now a large and growing seamount south of the island. KÄ«lauea probably has more years ahead of it than behind, starting perhaps 300,000 years ago.
The two volcanoes formed along different curving but parallel lines, the Loa and Kea trends, that erupt chemically different magma. This was recognized in the 19th century as a geometric pattern but was not identified chemically until the last half of the 20th century.
Giant submarine landslides, first recognized in the early 1960s, have peeled away from the west side of Mauna Loa, most recently about 105,000 years ago. No such giant slides are known at KÄ«lauea
The south or southeast flanks of both volcanoes are continuously moving southeastward a few centimeters a year owing to volcano spreading. Gravity is the principal cause, aided by intrusion of magma into rift zones.
The summit of each volcano sits atop a poorly understood pathway that transports magma upward from a melting site 100 km (62 miles) deep in the Earth’s mantle. A shallow reservoir system 2-5 km (1-3 miles) deep caps this pathway, and magma moves from there upward to the surface or into the rift zones that sprout laterally from the reservoir.
Most eruptions produce lava flows, a fact long known, but each volcano has violent explosive eruptions triggered by pent-up magmatic gas or steam from heated groundwater. Explosive eruptions are not unusual over a time horizon of centuries and need consideration in long-term planning.
These findings, far from exhaustive, are awfully impressive. All were acquired since the late 1950s and took major effort to amass the necessary evidence.
They result from research. Whether at a university or a volcano observatory, research is needed to better understand volcanism. The science can’t stand pat, arrogantly assuming that it already knows enough to suit society’s needs. To improve, we must always learn more.
Here are some important questions about Mauna Loa and Kīlauea that we can’t yet answer.
What are the details of melting in the mantle, and why does the supply rate of magma from the mantle to the shallow plumbing system change over time?
What will cause the next giant landslide from Mauna Loa and, perhaps, the first from KÄ«lauea?
Can we develop a way to determine how long an eruption, once underway, will last?
Can the next explosive eruption be predicted? How large will it be?
A new concept for KÄ«lauea is that periods dominated by explosive activity last centuries and alternate with periods of similar length dominated by lava flows. If so, when will the next explosive period start at KÄ«lauea? What clues might foretell it? When will it end?
Such questions drive research—with progress inevitable, if at times frustratingly slow.
