Understanding Katla Volcano in Iceland

Recent seismic activity in the region of Katla has led researchers to believe it will erupt again. In order to understand the potential hazards of new eruptions, researchers need to understand how these eruptions historically behaved. In their new paper titled Large Explosive Basaltic Eruptions at Katla volcano, Iceland: Fragmentation, grain size and eruption dynamics, Schmith et al. (2018) investigated why this volcano is so explosive. In order to do this, they used size, shape, and composition of the ash fall deposits from the eruptions in the 17th and 18th century.

Katla, one of most hazardous volcanoes in Iceland, is located in the southeastern part of the country (Fig. 1 & 2). The volcano lies 1450 m above sea level, and the caldera covers an area of nearly 110 km2. Katla is topped by the 230 m thick Mýrdalsjökull glacier which covers an area of ~ 600 km2, which melts and causes lahars and flooding during eruptions. Katla has a history of major explosive eruptions that occur on average about every 50 years. These eruptions are sometimes large enough that ash falls on mainland Europe, including during the 1625 and 1755 CE eruptions.

The 2010 Eyjafjallajökull eruption in Iceland was small compared to past eruptions of Katla, yet airspace in 20 countries was closed for 5 days to commercial air traffic, ~ 10 million travelers were affected, and the world’s average temperature fell by 1 ℃. A future Katla eruption is predicted to be ten times larger than the 2010 Eyjafjallajökull eruption. Heat from Katla causes glacial outburst floods when parts of the Mýrdalsjökull glacier melt and breach the crater of the volcano creating large lahars. During the last major eruption of Katla in 1918, the lahar produced was so large that it extended Iceland’s coastline in the region by 5 km (Katla’s Hazards, 2019).

Figure 1: A: Iceland with the region of interest shown in the red box. B: Zoomed in view of the region of interest showing locations of the Eyjafjallajökull, Katla, and Surtsey volcanoes in southeastern Iceland. Satellite imagery courtesy of Google Earth.

In order to understand the mechanisms of past eruptions and the extent of magma/water interactions, the researchers first turned to ash deposits. They evaluated the amounts of tachylite (heterogeneous glass), sideromelane (homogeneous glass), lithics (rock pieces), or crystals. By understanding the amounts of each of these are present in the ashfall, scientists can infer whether the explosivity of an eruption is more fragmentation/gas dissolution driven or driven by interaction of water and magma to cause explosive steam and lava eruptions.

Figure 2: Volcanic ash from previous eruptions found within the Mýrdalsjökull ice. Figure from British Geological Survey (Katla volcano, 2019).

Next, Schmith et al. (2018) determined the extent of fragmentation at the time of the eruption. As magma rises to the surface, gasses dissolved in the magma begin to come out of dissolution and form bubbles. As the magma rises further the bubbles expand more and more until there are more bubbles than magma, resulting in fragmentation. When the bubbles all finally pop, an explosive eruption occurs. This process is similar to opening a shaken bottle of soda. When you open the bottle the pressure is decreased and bubbles begin to form. The bubbles degassing rapidly cause the soda to explode. By understanding the fragmentation process of the Katla volcano, geologists can infer past and future eruption sizes.

Finally they determined the water/magma interaction of glacial meltwater of the 1625  and 1755 eruptive events. To this end they examined the size and sorting of the ash grains. A decrease in grain size and increase in the sorting of ash indicates a decrease in the ash column height.  A decrease in grain size with a decrease in sorting of ash grains indicates increases in fragmentation intensity (Fig. 3).

Figure 3: Plots showing grain size base on median size (φ) in each unit vs. sorting. Figure adapted from Schmith et al., 2018.

Overall Schmith et al. (2018) found that both the 1625 and 1755 ash deposits were composed mainly of the two glasses, tachylite and sideromelane, followed by crystals and lithics (Fig. 4), which indicates that the eruptions were not water driven.

Schmith et al. (2018) found that 1625 CE eruption was a combination of magmatic degassing and water/magma interaction (phreatomagmatic) and  that the water/magma interaction generally decreased over the course of the eruption. However, toward the end of the eruption, the water/magma interaction became the larger driver of the eruption over fragmentation.

Figure 4: Components of ash fall deposits for the 1625 and 1755 Katla eruptions. Figure from Schmith et al. (2018).

The 1755 CE eruption was similar to the 1625 eruption in that it was both a result of fragmentation and of water/magma interaction. However, in the case of this eruption the water/magma interaction was only dominant at the beginning of the eruption, and fragmentation dominated most of this eruption.

By understanding how water from the glacier interacts with lava and superheated material, scientists can use the data from this study in order to help predict potential mechanisms for future Katla eruptions. This will allow insight into how far the ash from an eruption might travel, and the extent of lahar flows and flooding. Understanding the dynamics of Katla and the Mýrdalsjökull glacier allows governments to plan for hazards resulting from a Katla eruption and put protections in place to help keep the residents of Iceland and mainland Europe safe.

References

Katla’s Hazards Katla Volcano, http://katlavolcano.weebly.com/katlas-hazards.html (accessed March 2019).

Katla volcano, Iceland | Volcanology | Icelandic volcanism | Our research | British Geological Survey (BGS), https://www.bgs.ac.uk/research/volcanoes/katla.html (accessed March 2019).

Schmith, J., Höskuldsson, Á., Holm, P.M., and Larsen, G., 2018, Large explosive basaltic eruptions at Katla volcano, Iceland: Fragmentation, grain size and eruption dynamics: Journal of Volcanology and Geothermal Research, v. 354, p. 140–152, doi:10.1016/j.jvolgeores.2018.01.024.

Cool carbonate volcano in Africa, Ol Doinyo Lengai… No really, it’s cool!

Figure 1: The Arusha province of northern Tanzania is outlined in pink. White line through center is the border of Tanzania and Kenya. Ol Doinyo Lengai marked with yellow marker. Image courtesy of Google LandSat imagery (2018).

Ol Doinyo Lengai, or “Mountain of God”, is an active stratovolcano located along the East African Rift (EAR) in the Arusha volcanic province of northern Tanzania (Fig. 1 & 2). This volcano is unique in a few different ways: 1) it erupts carbonate material, rather than the usual silica rich material,  2) typical eruptions are extremely effusive, resembling black water more than lava flows; 3) the lavas are very cool compared to other lavas, at ~ 510℃ compared to 1171℃ at Kilauea; and 4) solidified lava weathers rapidly and turns white (Fig. 3).

Figure 2: Ol Doinyo Lengai volcano. Water stream in foreground. (By Clem23 - Own work, CC BY-SA 3.0)

For the past century Ol Doinyo Lengai has been erupting lavas that are uniquely poor in silicate minerals yet enriched in sodium, potassium, and rare earth elements (REE) such as rubidium, strontium, zirconium, niobium, thorium, and uranium. The most common type of lava on Earth today is basalt. Basalts typically contain 45 - 55% silica (SiO2). The carbonatite eruptions of Ol Doinyo Lengai contain <20% SiO2. So where is this cool, silica poor, REE-enriched lava coming from? This is a question scientists have been trying to answer since the discovery of this volcano. Mollex et al. (2018) may have new answers in their paper “Tracing helium isotope compositions from mantle source to fumaroles at Oldoinyo Lengai volcano, Tanzania.”

Figure 3: Satellite imagery of Ol Doinyo Lengai. The white is not snow. It is weathered carbonate material from previous eruptions. (Image courtesy of Google Maps satellite imagery.)

Helium has two stable isotopes: 3He and 4He. 3He was made during the Big Bang, and as the Earth formed it became incorporated into the mantle. 4He is a product of alpha decay of Uranium and Thorium. By studying the relative abundances of 3He and 4He in lavas, scientists can infer where the magma originates. In the Earth’s atmosphere  the ratio of 3He / 4He is 1.384 x 10-6, while crustral ratios are 0.4 to 1 x 10-8. The 3He / 4He ratios are typically reported relative to the atmospheric level as R/RA. In these units crustal rocks typically have 0.01 to 0.1 R/RA, and mantle rocks have 5 - 50 R/RA (Emsley, 2001) (Fig. 4). Mollex et al. (2018) sampled rocks, fumaroles, and cognate xenoliths1 in order to find the 3He/4He ratios of Old Doinyo Lengai.They found that the helium isotope compositions from cognate xenoliths at the summit of the volcano ranged from 5.79 ± 0.82 RA  to 7.24 ± 0.44 RA (Fig. 5). These ratios closely match those of more traditional silicic volcanoes of the surrounding Arusha volcanic province.

Figure 4: 3He/4He ratios found on Earth and in the solar system. Around 10-5 are Ocean Island Basalts (OIB), Mid-Ocean Ridge Basalts (MORB), and Island Arcs (Arcs). Figure 12.1 from White (2015).

Figure 5: Helium isotope ratios from previous studies (left) and the current study of Mollex et al., 2018 (right). RC / RA are helium isotope ratios corrected for atmospheric contamination. SCLM is Subcontinental Lithospheric Mantle (shallow mantle), and MORB is Mid-Ocean Ridge Basalt. The typical ratios of Typical 3He/ 4He ratios for SCLM are shown in orange (Gautheron & Moreira, 2002). And typical 3He/ 4He for MORB are shown in yellow (Graham, 2002). Gray circles denote uncorrected 3He/ 4He ratios. (R / RA). Figure 4 from Mollex et al. (2018).

Based on the helium isotopic ratios found in rocks and summit fumaroles on Ol Doinyo Lengai as well as other volcanoes in the Arusha volcanic province, Mollex et al. (2018) believe that the magma source may be the same for both. They propose that the magma source is old enriched sub-continental lithospheric mantle (SCLM) that has undergone compositional changes from fluids or a mid-ocean ridge basalt (MORB) type mantle magma that mixes with the Ol Doinyo Lengai magma chamber.

The research of Mollex et al. (2018) sheds more light on this enigmatic volcano but more work is required in order to fully understand what is happening in the complex magma system beneath Ol Doinyo Lengai.

References

Emsley, J., 2011, Natures building blocks: an A-Z guide to the elements: Oxford, Oxford University Press.

Mollex, G., Füri, E., Burnard, P., Zimmermann, L., Chazot, G., Kazimoto, E.O., Marty, B., and France, L., 2018, Tracing helium isotope compositions from mantle source to fumaroles at Oldoinyo Lengai volcano, Tanzania: Chemical Geology, v. 480, p. 66–74, doi:10.1016/j.chemgeo.2017.08.015.

White. W.M., 2015, Chapter 12 Noble Gas Isotope Geochemistry, in Isotope Geochemsitry, New York, Wiley-Blackwell, p. 418-452.

How lava flows on Olympus Mons tell us about the volcanic history of Mars

When we think about big mountains on Earth, the first thing that comes to mind is almost always Mt. Everest. Everest, however, is absolutely miniscule in comparison to the solar system’s largest volcano, Olympus Mons.

Standing at 21,229 meters above the Mars global datum (which can be thought of like sea level here on Earth), Olympus Mons is about two and half times as tall as Mount Everest. Unlike Everest, which is the result of two continental plates slamming into each other, Olympus Mons has a volcanic origin. It can be classified as a shield volcano, similar to those that make up the Hawaiian Islands.

Shield volcanoes are characterized by broad, gentle slopes (4-8 degrees) and tend to erupt nonviolently out of fissures on the flanks of the volcano (think the recent lava flows in Hawaii). The tops of shield volcanoes tend to have calderas, which are large collapsed structures found at the top of volcanoes. The magma in the chamber provides pressure that effectively holds up the top of the volcano.The magma chamber is literally inflating the top of the volcano, sustaining its dome-like shape. When the volcano is done erupting and the chamber is partially empty, the top of the volcano collapses and forms a caldera. Things can get a bit more complicated, however, as has been recently discovered at the caldera at the top of Olympus Mons.

Figure 1: The caldera atop Olympus Mons. Colors correspond to elevation, where warmer colors are higher and cooler colors are lower. The blue shapes extending outwards in almost all directions are lava flows. From Mouginis-Mark and Wilson (2019).

The caldera atop Olympus Mons, like the volcano itself, is huge. Its horizontal dimensions are 60 X 80 km, and it has a depth of about 3 km. Lava flows radiate outwards from the rim of the caldera (Fig.1). The strange thing about this caldera, however, is that some of these lava flows appear to flow uphill (Fig. 2). This is not normal, even on Mars. Lava can sometimes travel small distances uphill due to confining pressure or momentum. The lava flow on Olympus Mons, however, didn’t travel a short distance uphill -- it appears to have gone several kilometers!

Figure 2: Zoomed in from figure 1 to show the anomalous lava flow. The left and right images show the same lava flow. The left is CTX image of the flow and the right is an interpreted sketch of the flow with contour lines. The arrow denotes flow direction. Notice how the flow travels uphill. From Mouginis-Mark and Wilson (2019).

Scientists have instead interpreted this to mean that the lava flow was emplaced and flowed downhill normally, cooling as it did so. Later, new magma was brought up to the near surface through cracks in the rock in a sheet-like intrusion, called a dike. This dike caused a localized inflation to occur within the caldera which tilted certain areas. One of those areas was near the lava flow, making it appear to be flowing uphill. But why is this significant? This tilting shows scientists that volcanism didn’t end when previously thought, when the caldera collapse occurred. Instead, there must have been renewed volcanism closer to the present. By understanding the timing of volcanism on Mars, we can better understand Mars’s evolution as a planet, and therefore what past conditions on Mars could have been like. Was Mars more volcanic in its past? Could this volcanism provide a greenhouse effect to allow life to exist? This work takes us one step closer to fully answering these questions.

Original paper:

Mouginis-Mark, P. J., & Wilson, L. (2019). Late-stage intrusive activity at Olympus Mons, Mars: Summit inflation and giant dike formation. Icarus, 319(September 2018), 459–469. https://doi.org/https://doi.org/10.1016/j.icarus.2018.09.038

Investigating the Hazards of an Underwater Volcano: Could Kick ‘em Jenny Produce a Tsunami?

When you imagine volcanic hazards, you might think of dramatic scenes of lava flows inundating neighborhoods, such as the 2018 lava flows in Hawaii. The thing is, not all hazardous volcanoes have people living on them. In fact, some of them are erupting, growing, and collapsing underwater, yet can still pose a significant hazard to people. Displaced water due to submarine landslides are capable of  producing hazardous water conditions, including tsunamis. GPS equipment and satellite imagery make it relatively easy to continuously monitor changes in volcanoes above the ocean. However, it’s a much different story for volcanoes below the ocean’s surface, since satellite images cannot be taken and GPS signals cannot transmit through water.  This obstacle makes collecting continuous real-time data about how these underwater features are changing almost impossible. Instead we rely on periodically-deployed unmanned submarines to create seafloor maps using lasers (Figure 1). This process is called bathymetric surveying. These surveys are expensive to conduct, time-intensive, and may require scientific equipment that is difficult to acquire. This means that often many years pass before a new set of data can be collected.

Figure 1: Figure 3  from Allen et al. (2018) showing a 3D projection of a bathymetric map collected at a set of caribbean underwater volcanoes. The numbers mark the locations of features related to the volcano including: (1) collapse features, (2) Kick ‘em Jenny volcanic cone, (3) Kick-‘em-Jack volcanic cone, and (4/5) volcanic debris.

Figure 2: Map showing the the location of Kick ‘em Jenny with a red pin (Google Maps, 2018).    

Kick ‘em Jenny (Figure 2)  is an underwater volcano in the Caribbean that is thought to be named by sailors who noticed that the waters around it were often quite rough, presumably due to the changing landscape of the seafloor. Researchers (Allen et al., 2018) investigated the modern history of the underwater volcano by comparing the bathymetric data (i.e. underwater elevation) from 1984, 2003, 2013, 2016, and 2017 in an effort to identify possible risk. They wanted to identify where and how regions of the volcano were growing or collapsing. They did this by looking at the difference between datasets to isolate areas that had changed and measure how much change had occurred.

Figure 3: Figure 5 from Allen et al. (2018) showing areas where the volcano grew (red) and areas where the volcano experienced collapse or landslides (blue) between each timestep.

Their results (Figure 3)  allowed them to determine whether or not Kick ‘em Jenny was likely to produce a significant tsunami event. They did this by figuring out approximately how much material has been moved during landslide events, which allowed them calculate how large of an impact those landslides could have at the surface of the water. They also determined a worst-case scenario for the largest landslide event that the volcano is capable of producing and calculated the size of the waves that such an event would produce. Their results came with good news for people living on the Caribbean islands: it would actually be unlikely for this volcano to produce waves at the water's surface that could pose a significant threat to people on land. In their worst-case scenario, their models showed that the nearby island of Grenada could possibly experience waves as high as 6 meters tall, and waves would be around 1 meter tall by the time they reached Puerto Rico. This means that Kick ‘em Jenny doesn’t pose a widespread tsunami threat, but lower elevation areas along Grenada’s west coast could be affected, particularly near beaches along the southwest portion of the island. The largest event that they have evidence for in modern history is about 30x smaller than the worst-case scenario and so they determined that volcanic hazard monitoring should focus on how tumultuous waters might impact ships traveling through the region.

References

Allen, R. W., et al. "30 Years in the Life of an Active Submarine Volcano: A Time‐Lapse Bathymetry Study of the Kick‐'em‐Jenny Volcano, Lesser Antilles." Geochemistry, Geophysics, Geosystems 19.3 (2018): 715-731. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GC007270

Google Earth, “Kick ‘em Jenny.” (2018). https://goo.gl/maps/9rVnV7n3LHy