ARE YOU CATCHING MY RIFT?
This Earthcache will physically take you to the site of the 2018 eruption of Kilauea's East Rift Zone that occurred from May 3 to September 4 within the Leilani Estates subdivision. Fortunately, no lives were lost during this epic upheaval, but over 700 homes were destroyed as the area sustained $800 million dollars worth of damage. Your observations of the aftermath of this volcanic eruption will help you better understand what a rift zone is and how it can impact human life.
Volcanic Rift Zones
The rift zone of a volcano is an area where it is "rifting" or splitting apart. It can be thought of as a crack in the flank of the volcano where the rock is weak and magma can easily escape. Rift Zones, like volcano summits, are very prone to erupting.They form underground tunnels extending miles away from the central magma storage chamber. Basaltic shield volcanoes typically have 2-3 rift zones radiating away from the central magma chamber. Often the rift zones have 120° of separation. Although Kilauea and Mauna Loa are both shield volcanoes, each volcano has only two rift zones. The East Rift Zone of Kilauea is longer than it's Southwest Rift Zone, extending about 31 miles on land and another 43 miles below sea level. Historically, it is also more active than the Southwest Rift Zone.
Volcanic Fissures
Fissures are linear volcanic vents typically found along the rift zones of shield volcanoes. Although they are usually only a few meters wide, they can be several kilometers long. Lava eruptions at fissures are rarely explosive. Instead, fissure vents like those found on Kilauea's East Rift Zone, produce spectacular "curtains of fire." This is when many lava fountains can be seen erupting in a line stretching down the rift. These fountains build up low ramparts of basaltic spatter on both sides of the fissure, leaving trench like formations when the lava hardens after the eruption ceases.
Fountains that are more isolated along the fissure produce small spatter cones or larger cinder cones. With time, rift zone eruptions tend to become focused at just a few or only one single spatter cone.
2018 Eruption of Kilauea's Lower East Rift Zone
In March of 2018, Kilauea was erupting at it's summit as well as 12 miles further down the East Rift Zone at the Pu'u O'o volcanic cone. This activity was part of an eruption that had been taking place for 35 years. But then on April 30th, Pu'u O'o collapsed! Simultaneously, magma began to drain out of the Kilauea summit. All of this magma pushed another 13 miles deeper into the East Rift Zone, putting pressure on the magma chambers beneath Leilani Estates. On May 3, the first fissure opened, fountaining lava in a residential area. On May 4, a 6.9 earthquake rocked Hawaii Island, widening the underground magma conduit leading to Leilani Estates by 8 feet!
By May 27, 24 fissures had opened and erupted fountains of lava in a straight line through Leilani Estates and a neighboring subdivision. Some lava fountains reached heights of 300 feet. By the end of May, nearly all eruptive activity was concentrated at Fissure 8, whose cone formation peaked at a height of 180 feet. On June 4, a lava channel issuing from Fissure 8 reached the ocean, destroying the small town of Vacationland Estates and eventually completely filling in Kopoho Bay. This entire event was the most destructive volcanic activity in the United States since the eruption of Mt. St. Helens in 1980.
Types of Volcanic Cones
Material that erupts from a volcanic vent piles up around it and forms a triangle shaped hill known as a cone. There are four major types of volcanic cones:
1) Composite Cones (also known as stratocones) are the iconic image most people think of when they hear the word volcano. They often have peaks that are several thousand meters high and rise very steeply above the surrounding landscape. Composite cones are made of layers of volcanic ash, lava, and rock fragments deposited over time after repeated eruptions which tend to be violently explosive. Mt. Fuji in Japan is a classic example of this cone type. 2) Cinder Cones (also called pyroclastic cones) are the most common type of volcanic cone. They form when lava gets blown violently into the air and hardens into gravel sized pieces before falling back to the ground and piling up around the vent as "cinders." Cinders are light weight because the lava hardens around tiny bubbles of trapped gas making them extremely porous. Cinder cones can be tens of meters to hundreds of meters tall and many are seen on and around Mauna Kea. 3) Spatter Cones often form in areas of minor volcanic activity and can appear in lines along volcanic fissures. They form when blobs of thick, viscous lava are ejected and pile up around the vent before the lava has cooled. This activity results in the formation of small, steep sided cones that are typically 1-5 meters tall. 4) Tuff Cones are also known as ash cones. They form when lava comes into contact with a large body of water. The water becomes super heated and flashes violently into steam which explosively fragments massive amounts of lava into plumes of fine ash. This ash rains down around the vent forming an ash cone, which over time, gets weathered into rock called tuff. Tuff cones have steep sides and extremely broad craters. Diamond Head, on the island of Oahu, is a famous example of a tuff cone.
QUESTIONS:
1) Looking at the map of the rift zones of Mauna Loa and Kilauea, why do you think these shield volcanoes have only 2 rift zones?
2) At the GZ, it's pretty evident that you are standing on a volcanic rift zone. Please describe what you see. List three features of the landscape that indicate underlying volcanic activity.
3) At the GZ, you are standing a few feet from the remnants of Fissure 9. What type of volcanic cone is Fissure 9? Why did you choose this answer? Moving to the waypoint and looking east, you can see Fissure 8 in the distance. What type of volcanic cone is Fissure 8? Why did you choose this answer?
4) As proof of having visited the GZ, please send a picture of yourself or your group with Fissure 9 in the background. You may log this find immediately after messaging me with the answers.
REFERENCES:
https://www.geologyin.com/2018/05/whats-beneath-kilauea-hawaiis-most.html
https://www.usgs.gov/news/volcano-watch-getting-rift-zone-why-and-how-they-erupt
https://hilo.hawaii.edu/natural-hazards/volcanoes/riftzones.php
https://en.m.wikipedia.org/wiki/Rift_zone
https://en.m.wikipedia.org/wiki/Fissure_vent
https://www.nps.gov/havo/learn/nature/2018-eruption.htm
https://hilo.hawaii.edu/natural-hazards/offmain/2018KilaueaEruption.php
https://en.m.wikipedia.org/wiki/2018_lower_Puna_eruption
https://education.nationalgeographic.org/resource/types-volcanic-cones/