Everything You Need To Know About Kilauea’s 2018 Eruptions: Part I

Before I was interested in meteorology, I was fascinated by volcanoes. Even as early as preschool, I would religiously watch my many volcano VHS tapes, and I’d make my parents read this book to me. I was particularly fond of the Hawaiian volcanoes because the lava was so colorful, so my 5-year-old self was beyond thrilled when my folks told me that we were taking a vacation in Hawaii and would have some time to check out Hawaii Volcanoes National Park.

Of course, I became infatuated with the idea of seeing the elusive “hot lava” flowing from the volcanoes and was frankly disappointed with our trip to Hawaii Volcanoes National Park, at least initially. I was expecting to be greeted by a lava lake the size of the Kingdome, so it was quite the letdown for me when all I saw was just a bunch of smelly steam vents. And to make matters even worse for my parents, I had a full-on meltdown when some state troopers closed off the route we were driving on due to lava flowing over the road and into the ocean a couple miles away. I simply lacked the capacity to understand why my parents wouldn’t heed my advice and speed past them so I could see the hot lava. But all-in-all, I had a wonderful time and it was really cool to see how the lava flows shaped the landscape, even if I didn’t get an eyewitness account of any hot lava.

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Unless you’ve been living under a lava bed, you’ve heard of the dramatic increase in volcanic activity at Kilauea this month. But one thing that you might not know is that Kilauea has been continuously erupting for the last 35 years. Pu‘u ‘Ō‘ō, a volcanic cone in Kilauea’s East Rift Zone, first began erupting on January 3, 1983, and it hasn’t stopped since.^[1] This current episode is known as the “2018 lower Puna eruption,” and it began when a magnitude 5.0 earthquake opened up group of fissures in the Leilani Estates subdivision along Kilauea’s East Ridge Zone on May 3.^[2] It is the 62nd unique episode of heightened activity since the Pu‘u ‘Ō‘ō eruption began in 1983.^[43]

There’s a lot to cover, so I’m gonna split this writeup into two blogs. In this blog, I’ll discuss how the Hawaiian Islands formed, how Kilauea differs from the explosive stratovolcanoes like those that dot the Cascade range, and the chronology of the Pu‘u ‘Ō‘ō eruption itself. Blog number two will be a summary of the 2018 lower Puna eruption. Grab a bag of popcorn, turn on your lava lamp, and get ready of an educational adventure – I hope you learn as much reading this blog as I did writing it.

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The Hawaii Hotspot

Volcanoes generally form at three types of locations: convergent oceanic plate boundaries (either oceanic/oceanic or oceanic/continental – the Aleutian Islands and Cascades are good examples respectively), divergent plate boundaries such as the Mid-Atlantic Ridge and East African Rift Valley, and “hotspots” such as Hawaii, Yellowstone, or Iceland. A “hotspot” is technically defined as a region of volcanism under a “mantle plume,” which is a region of the Earth’s mantle with a temperature warmer than that of the surrounding mantle. Due to thermal expansion, the warmer region of the mantle is less dense than its surroundings and thus convects outward towards the Earth’s lithosphere, which is composed of the solid, uppermost part of the mantle and crust and is split into numerous tectonic plates that glide along the asthenosphere, a deeper, warmer, and more ductile part of the mantle. Because the mantle is a ductile solid, this convection happens on geologic time scales, but it happens nonetheless.

When this mantle plume reaches the lithosphere, it melts parts of the lithosphere into magma. The thickness of the lithosphere varies from just a few kilometers near mid-ocean ridges to over 200 km over large, old continental plates.^[3] The Hawaii Hotspot’s magma chamber is estimated to lie approximately 90-100 km below the surface.^[4]

Though the existence of mantle plumes is generally accepted, there is still some disagreement as to whether these plumes (and their resulting hotspots) remain stationary with respect to the Earth’s mantle or move over time. J. Tuzo Wilson, the Canadian geophysicist who first proposed the idea of hotspots and mantle plumes, postulated that these mantle plumes remain relatively stationary over time while tectonic plates glide over the top of them.^[6] This makes sense when looking at the Hawaiian Islands – the Big Island is currently under the hotspot and is experiencing volcanism, and each subsequent island to the northwest has older rock and is more heavily eroded. Additionally, other hotspots on the Pacific plate same plate are more-or-less parallel to each other, further supporting the notion that these mantle plumes remain stationary over time.^[7]

However, if you look at the chain of islands and seamounts that have formed due to the Hawaii Hotspot, you’ll notice a very sharp bend to the NNW in the Northern Pacific. It was previously thought that this bend was due to a sudden change in plate direction, but a more recent study by John Tarduno et. al ^[9] found no tectonic evidence supporting a shift in plate direction and, by analyzing how grains in magnetite had aligned themselves with the Earth’s magnetic field (which is itself a function of latitude), deducted that the reason for this shift was that the Hawaii Hotspot itself was drifting southward but suddenly stopped drifting around 47 million years ago and has remained relatively stationary since.^[9] The bottom line is that there is still a significant amount of disagreement in the scientific community as to what caused the bend, and it is very possible that both a change in hot spot position and tectonic plate movement were responsible for the bend.^[10]

The further northwest you go from the Hawaii Hotspot, the older and more heavily eroded the islands are. The “Northwestern Islands” to the northwest of Kaua’i and Ni’ihau have a very different appearance than the “Southeastern Islands” we are more familiar with.^[11]

Nihoa and Necker are small islands, but the rest are atolls, which are ring-shaped coral reefs that build upon an existing underwater structure and rise above land to create a protected lagoon. Notice the difference between Nihoa to the SE and Kure to the NW.^[12]

Northwest of Kure, the islands have degraded so much that they can no longer support atolls but have instead become seamounts. The oldest seamounts are near the convergence of the Kuril-Kamchatka and Aleutian Trenches, and the very oldest of these, the Meiji Seamount, is approximately 85 million years old!^[16][17] It is likely that other, older seamounts have been subducted under these trenches, so the Hawaii Hotspot has been active for at least 85 million years and potentially much longer.

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To summarize, the entire Hawaiian-Emperor Seamount Chain was caused by the Hawaii Hotspot, which is a mantle plume that creates magma chambers when it encounters the lithosphere, the relatively cool and rigid outermost layer of the Earth that is split into tectonic plates. As these lithospheric plates move over the mantle plume, new islands are formed by volcanic activity. The Hawaii Hotspot is currently over the Hawaiian Island/Lōihi Seamount (a burgeoning seamount to the SE of Hawaii that is expected to surface in several tens to 100,000 thousand years.^[19]

Convergent/Divergent Plate Boundary Volcanoes

I’ll spend significantly less time covering these since they are not the focus of this blog; I’d just like to show how hot spots differ from these regions of volcanic activity. Both are caused by the movement of tectonic plates.

Convergent Plate Boundary Volcanoes

If you are from the Pacific Northwest, you are familiar with convergent plate boundary volcanoes due to a subducting lithospheric plate, as all of our local volcanoes are formed by this mechanism. These volcanoes are formed when the subducting plate sinks at least 100 km below the surface and the high temperature/pressure releases gases trapped in the plate. As these gases move towards the surface, chemical reactions (as opposed to thermal, in the case of hot spots) melt the lithosphere, forming magma. This magma then rises to the surface, creating volcanoes.^[20]

Most of these volcanoes are “stratovolcanoes.” The magma under stratovolcanoes is much more viscous than the magma under the broad, gently sloping “shield volcanoes” that make up the Hawaiian Islands, and this characteristic leads to eruptions in the form of viscous lava flows, ash, tephra, and pumice.^[21] For this reason, stratovolcanoes are often called “composite volcanoes,” as their steep slopes are composed of a variety of volcanic materials.^[21] The slopes of shield volcanoes are almost exclusively composed of relatively fluid lava flows.

The composite layers of lava, ash, tephra, and pumice on stratovolcanoes help cut off various vents on the slopes of the volcano itself. As a result, the gases released by the magma building under the volcano cannot escape, and when enough pressure builds, the volcano erupts, often in catastrophic fashion. For example, the opening salvo to Mt. St. Helens’ 1980 eruption was a 0.7 cubic-mile landslide that rushed down the mountain at speeds of up to 150 mph through Spirit Lake, where it caused a 850-foot-tall megatsunami.^[22][23]

With the notable exception of an impressive 6.9 magnitude earthquake on May 4th, the most dramatic thing that has happened with the 2018 lower Puna eruption were some 100 meter tall lava fountains in the Leilani Estates area on May 5.^[24][25] Still, football-field-sized lava fountains are nothing to sneeze at… check out this awesome video of the fountains fromeck out this video from Bruce Houghton, Ph.D., a professor of volcanology at the University of Hawai’i.

Lava fountains 300 ft high during May 5 fissure eruption in Leilani Estates. https://t.co/W0qoOFPYV8 pic.twitter.com/TKKPjPLNQg

— USGS Volcanoes🌋 (@USGSVolcanoes) May 7, 2018

 

Divergent Plate Boundary Volcanoes:

Volcanoes also form at divergent plate boundaries, as magma rises through the mantle and creates new oceanic lithosphere to fill the void between these spreading plates. Most divergent plate boundaries are underwater and are in the form of mid-ocean ridges.^[28] A classic example is the Mid-Atlantic Ridge, which separates Eurasia/Africa from the Americas and first split these two in the Late Triassic Period some 235 million years ago.^[29]

The East African Rift is an example of a relatively new divergent plate boundary that has not been filled by seawater. The rift valley is dotted by tall and largely dormant volcanoes. The most famous of these is Mt. Kilimanjaro, a giant stratovolcano whose last major eruption was 150,000-200,000 ago.^[30]

Whew! Now that you know about the different ways that volcanoes can form, let’s learn about Kilauea’s Pu‘u ‘Ō‘ō eruption.

How Pu‘u ‘Ō‘ō Formed:

Wikipedia defines Mt. St. Helens as an active volcano, but even the most notorious stratovolcano in the United States can’t hold a candle to Kilauea when it comes to the frequency of volcanic eruptions. Kilauea’s magma chamber is filled with free flowing, low-viscosity molten rock that can easily escape to the surface, and Kilauea’s latest eruption began on January 3, 1983 and continues to this day.^[33]  For you baseball fans out there, you could say that Kilauea is the Cal Ripken Jr. of volcanic cones.

Puʻu ʻŌʻō was formed in the same manner as many volcanic cones on Hawaii, with magma bursting through a fissure formed along a rift zone.^[35] Though Kilauea has a summit caldera and an enclosed, currently active crater (Halemaʻumaʻu Crater), much of its magma actually flows along rift zones flanking the volcano, either making it to the surface through magma “dikes” or flowing directly into the ocean via lava tubes.^[36][37] These dikes are parallel to the rift zone and push it outward like a divergent plate boundary, creating new fissures as a result.^[37]

If you take a look at a satellite image of Big Island, you can see the pronounced rift zones on Mauna Loa in particular. It’s incredible how much of the island is part of Mauna Loa; having hiked on its slopes, I can attest that it feels much more like a gradual, never-ending hill than a 13,681′ foot peak.^[39]

Pu‘u ‘Ō‘ō’s Eruptive History:

The fateful fissure that opened up on Kilauea’s East Rift Zone on January 3, 1983 proved to be a particularly active one. Copious amounts of lava flowed out of fissures in the vicinity for the next couple months, but it wasn’t until June 1983 that the Puʻu ʻŌʻō cone began to form in earnest.^[33]

Over the next 36 months, there were 44 individual episodes at Puʻu ʻŌʻō. These episodes were generally less than 24 hours long, were characterized by spectacular lava fountains reaching up to 470 meters (1550 feet) high, and occurred at regular intervals of 3-4 weeks.^[33]

By June 1986, Puʻu ʻŌʻō was 255 meters high. Interestingly, the northeasterly trade winds resulted in the SW side of the cone being much higher than the NE side.^[33] When I think about the shape of cinder cones, global atmospheric circulation isn’t the first thing that comes to mind, but it makes perfect sense for a cone such as Puʻu ʻŌʻō.

July 1986 marked a new era for the Puʻu ʻŌʻō eruption, as the structure that supplied magma to Puʻu ʻŌʻō collapsed. Though some magma was still able to reach Puʻu ʻŌʻō, the primary eruption shifted two miles to the northeast. Instead of the periodic and spectacular lava fountains that were common at Puʻu ʻŌʻō, lava continuously flowed out of a broader vent given the name “Kūpaiʻanahā.” While most of this lava was confined to a lava pond and was directed out to sea by a lava tube, lava occasionally overflowed the pond, building Kūpaiʻanahā to a broad shield volcano 56 meters (180 feet) high in less than a year.^[33]

While the lava from Puʻu ʻŌʻō was primarily of the viscous and chunky a’a variety, the lava flowing out of Kūpaiʻanahā was the smoother and less viscous pahoehoe. These flows created significant lava fields across the region. In 1989, the lava tube directing lava from the lava pond at Kūpaiʻanahā to the ocean collapsed, redirecting lava above ground and inundating the community of Kalapana 12 km to the southeast.^[41]

Activity decreased through the early 90s, and Kūpaiʻanahā finally became extinct on February 7, 1992 in response to another series of fissures forming along the East Rift Zone. The eruption returned to Puʻu ʻŌʻō ten days later, but it retained the less volatile and more continuous quality that it had when it was at Kūpaiʻanahā, with pahoehoe flows covering the landscape and lava tubes directing lava down to the ocean. Of course, there were also some weak lava fountains from time to time to keep things interesting.^[40]

In late January 1997, the crater inside the Puʻu ʻŌʻō cinder cone collapsed, substantially enlarging and deepening it. Though crater collapses had happened many times before, the 1997 collapse was particularly large, with the crater floor dropping approximately 500 feet. In response, new fissures formed along the East Rift Zone, but these were only active for 22 hours. It wasn’t until late February activity resumed with the filling of the lava lake within the Puʻu ʻŌʻō crater.^[31][40]

The period from 1997 to the present day has been characterized by smooth pahoehoe flows that continue to build up the shield around  Puʻu ʻŌʻō and deposit lava into the ocean through lava tubes, with occasional new side vents and crater collapses to temporarily enhance activity and enlarge the size of the crater.^[1][31] While the current eruption at the Leilani Estates and nearby regions may seem to have occurred suddenly and out of the blue, it was initiated by a crater collapse at Puʻu ʻŌʻō and appears to simply be a high-impact and particularly vigorous episode within our current pattern.^[42]

Congratulations on making it to the end of this blog, and I hope you learned something! Look out for Part II in the next month or so, where I’ll give an in-depth overview of the 2018 lower Puna eruption!

Thanks for reading, and please share!
Charlie

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