Thursday, June 14, 2018

Comparing and Contrasting the June Hawai'i and Guatemala Volcanic Events

Eruption from Fissure 8 on June 10, 2018. Photo courtesy of County of Hawai'i Civil Defense Agency
Volcanic eruptions on the Big Island of Hawai'i and in Guatemala have recently taken center stage not only on the geologic front but in the national news as well. How do these two geologic settings compare and contrast?

Both locales are located in active volcanic zones and so eruptions are nothing new here. They both produce eruptions of lava and scoria (ash, pebble and boulder-size particles) that originate from magma within the crust. The term magma is used for melted rock still residing in the interior of the earth and the word lava is used when it finally erupts to the surface. That is the difference between those two words although occasionally you may hear reporters use each term in the opposite way.

Eruptive column from Volcano Fuego on June 3, 2018, image from Strange Sounds web site.
Guatemala

While the Hawai'ian eruptions are relatively gentle, the event that occurred in Guatemala on June 3, 2018 was quite explosive. To explain the difference between these two types of eruption styles, we need to look no further than the silica content contained in the different magma bodies. When more silica is contained in the melted rock, the more explosive eruptions can be. Silica adds viscosity (resistance to flow) to magma and the only way escape  route for the included gases found in all magma bodies is to explode violently. As the magma reaches near the surface, the gas expands, reaching a threshold and the only to escape the viscous substance is to explode outward. Thus the eruption on Fuego that sent a scoria cloud nearly 10 miles high.

Chart showing magma chemistry and resulting rock types, original from Wayne Ranney lecture slide 
The web site, Volcano Discovery has good, up-to-date information on Fuego's current activity. I also monitor the Smithsonian Global Volcanism Program for science information. These are both excellent sources but the Smithsonian site contains more detailed information. Check out the general information link on Fuego's home page for an interesting history of this volcano, including a reference to an earlier edifice that began growing on the same spot 230,000 years ago which collapsed in a massive debris-flow avalanche that ran 30 miles out into the Pacific Ocean! Check out this video from Knut Eisermann on FB for excellent footage of the June 3 eruption which, fortuitously for photographers, occurred around noon local time. The explosive eruption emitted ash and lava with a silica content of no less than 65% and as much as 75%. The rocks created from such chemistries are called dacite or rhyolite, respectively.

Three part diagram showing the assembly of the Central American microplate at 20 Ma, 12 Ma and 0 Ma (the present)
The setting of Guatemala is along the Pacific Ring of Fire, where ocean crust beneath the Pacific Ocean is sinking (geologists say subducting) beneath the edge of the Central American microcontinent. When this slab of ocean crust descends to between 60 and 100 miles, it begins to melt and then rises buoyantly through the crust. The subducting plate, called the Cocos plate, is rather long and melting along its edge causes these types of eruptions that occur from a line of volcanoes that stretch from central Mexico to northern South America. In reality, this geologic setting stretches intermittently from Alaska to Tierra del Fuego! Another great site to peruse about the scene in Guatemala on June 3 is called Strange Sounds and you can view images of it here.

Photo of Vulcan Fuego in January 24, 2017 from an area near the village of Esquintla, destroyed by the pyroclastic flow on June 3.  Photo by Don Webster
As a result of nearly 10-mile high scoria column, a deadly pyroclastic flow caused more than 100 human casualties and destroyed many villages around the perimeter of the volcano. Pyroclastic flows (literally fire fragments) are some of the most dangerous aspects from eruptions such as these. They form when rocks are blasted high into the atmosphere and then as they fall back to earth can be dense enough to trap escaping gases. The falling fragments, still glowing red hot, then ride downslope on a cushion of gas which lessens friction and the flows can reach speeds over 100 miles. See this NASA Earth Science web site that depicts the damaged areas as surveyed on June 4, 2018. This is part of their disaster program. One of the pyroclastic flows came through the valley where this photo was taken by a friend of mine in January 2017.

Kilauea

The Kilauea eruptions by contrast have become a rather benign spectacle because these eruption types are much less explosive. They issue  lavas with a lower silica content of around 45 to 55%. This is why we are all treated to fantastic images from helicopters and ground-based photographers who can approach the flows more closely and more readily. The rocks formed by magmas with this chemistry are called basalt and the many picturesque photos and videos of red-flowing lava rivers will ultimately cool to create basalt lava rock. (Basalt is the most common rock type on Earth's surface, covering up to 62% mostly on the ocean floors of the planet).

Hot spot track in cross-section, by Joel E. Robinson, USGS, via Wikimedia Commons
Hawai'i is situated over a hot spot in the mid-Pacific (see diagram above). The Pacific plate is slowly drifting northwest over this comparatively stationary hot plume, causing eruptions in Hawai'i to shift through time in the southeast direction. Think of a smoke stack at a factory as the stationary hot spot and the wind-drifted smoke column as the chain of volcanoes through time. Around 5 million years ago, the island of Kaua'i was positioned right over the current eruptive center. But as time has passed, this area has drifted northwest about 300 miles, riding on top of the Pacific plate. One day, the Big Island will also become volcanically dormant and new islands will be present to the southeast. In fact another volcano is nearing sea level from below and is already 13,000 feet high (but still about 3,000 feet below sea level). It is called Lo'ihi and can be seen on the far right in the diagram above. Lo'ihi will likely merge with the Big Island, or it could become a separate island.

Space view of Kilauea volcano and the newly formed Fissure 8. From Nature Journal, June 9, 2018
The modern hot spot resides beneath the Kilauea volcano on the Big Island. The nearby Mauna Loa volcano is not quite inactive yet, but has moved far enough away that eruptions today typically come from the Kilauea cone. Three other volcanoes exist to the northwest on the Big Island and are considered inactive due to plate drift away from the hot spot. Anyone who lives on the flanks of the Kilauea volcano knew that they were rolling the dice with respect to life and property. Whereas the Guatemala eruption killed over 100 people, no one had died from this eruption in Hawai'i. The relative lack of silica in these lavas is the reason. However, rivers of lava have destroyed over 700 homes and the pain and suffering involved with this natural event cannot be discounted.

Map of lava flow paths from Fissure 8, depicting the extent of lava flows on June 11.
 Note the new land that has formed as a result of this event. From
Lava flows from Fissure 8 entering the sea. From Dr. Larry Freisen, Santa Barbara City College.

A well-known coral reef was destroyed here in Kapoho Bay. From Dr. Larry Freisen, Santa Barbara City College.
Tools

There are incredible videos to watch and a few are listed here.

To see a live stream video linked to the website of the US Geological Survey, with real time images of the lava flow click this link here.

A helicopter overflight of Kapoho Bay from the USGS on June 5, 2018 around 5 PM HST can be seen here.

Really good helicopter photos of the lava overtaking roads, and homes being engulfed here.

Don't miss this one! A 15 minute video of driving to the lava front on the day 500 homes were lost in Kapoho Bay. Incredible footage here!

Also, friend Nancy from the Big Island sent a link to a blog from a local there who describes many of the included photos in native Hawai'ian themes here. Updated regularly.

Geology is dynamic as these two events show. All of these kinds of events have happened millions of times in the past and will continue into the future. Knowing how the earth works can help our society prepare for future perturbations in a world that we would like to be predictable. Geology informs society.

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