Introduction The Kilauea volcano, the second-youngest volcano in the Hawaiian Ridge, has continued to have a significant impact on the surrounding environment and its population since its current phase of eruption started in 1983. This eruption is thought to be the longest-lasting in Kilauea’s entire history – a history between three-and six-hundred thousand years long.
It is also a history that has also literally produced the island of Hawaii itself, due to the shield volcano’s gently sloping sides, which constitute fifteen hundred square kilometers, or nearly fourteen percent of the Hawaiian island (USGS, 2017)In considering the geographical impact of Kilauea – its impact on its natural and human environments – this essay traces the development of volcanoes in general, and then turns its attention to the Hawaiian volcano specifically. It first discusses the definition of and processes behind volcanoes, focuses further on the formation of the Hawaiian Ridge – of which Kilauea is a part – and then considers Kilauea to assess the impact it continues to have today. VolcanoesA volcano is defined as being “an opening on the surface of a planet or moon that allows material warmer than its surrounding to escape from its interior” (NASA, 2008), and their evolution on Earth has contributed to the formation of the diverse landscapes that make up the planet (Okubo et al, 1997).
Volcanoes are typically formed at the convergence or divergence of tectonic plates – particularly on the sea floor – where friction melts layers of the Earth’s crust, creating magma chambers. In some places the Earth’s crust is about 19 miles thick; on Hawaii, the oceanic crust is only 3 miles thick (Robertson, 2011). Tectonic movement, pressure and geochemical reactions deep beneath the Earth’s surface generate the molten rock found in volcanoes. Pressure beneath the Earth’s crust (where molten rocks form), beyond the ‘Moho’ (the Mohorovi?i? discontinuity, which varies from about 5 miles to 25 miles beneath the surface), is immense: about 10,000 Earth atmospheres (1 Gigapascal, GPa).
Within the magma chamber, it is about 0.3GPa (USGS, 2014). Faults and fissures in the Earth’s crust release pressure; molten rock at depth can cause fracturing, too (Perez, 1999). Pressure release from the magma chamber causes the eruptions seen at volcanoes, which may be sudden and short, or slow and long-duration, depending on the geochemistry of the molten rocks.
The presence of water also affects magma characteristics. Most volcanic activity on the Earth’s surface occurs in oceans, due to the plate boundaries on the ocean floor (Okubo et al, 1997).During an eruption, lava, volcanic bombs, ash and gases are discharged, all of which have a profound effect on the surrounding landforms, ecosystems and geography. Ash landslides leave their mark on the landscape, burying everything in their path. Consequences for human populations living nearby can be devastating, causing sudden evacuations and temporary food shortages (Rubin, 2013). Explosive eruptions (such as that witnessed in Pompeii, 79AD) can be threatening and even fatal – to entire cities – generating clouds of hot ash that can spread hundreds of meters, demolishing anything in their path.
The ash lands like powdered snow; where it mixes with water from streams, mudflows form, which can bury and suffocate whole communities (Mattox et al, 1993). When taken into the upper atmosphere, ash clouds can severely affect air quality over a wide area and impair visibility for international air traffic.While precise prediction of volcanic eruptions is not possible (due to the very complex interplay of geochemistry, tectonics and climatic factors), continual survey and monitoring of known active volcanoes is a vital task to mitigate the hazards and threats to nearby populations and ecosystems.
The Hawaiian Ridge: a volcanic hotspot Figure 1: TITLE (Mattox, 1993)The Hawaiian volcanoes are located on the Pacific plate, created by the movement of the Pacific plate over a fixed hot-spot – like a fixed candle burning a hole through a moving sheet. The oldest, Kauai, stands together with Oahu; Maui and Hawaii are more recently formed. These volcanoes together make up the Hawaiian Ridge, which is formed from the region’s solid dense rock. The Hawaiian Islands are each composed of at least one central volcano.
The distinct island, known as the Big Island, is made up of five primary volcanoes which include Kilauea, Mauna, Loa, Mauna Kea, Hualalai and Kohala (Rubin, 2007). Each volcano has distinct characteristics. Mauna Loa is known as the largest volcano on Earth, while Kilauea is one of the most active and productive. Currently, only three of Hawaii’s volcanoes are active: Mauna Loa, Loihi and Kilauea. Kilauea has been erupting since 1983, while the Mauna Loa and Loihi volcanoes ceased erupting in 1984 and 1996, respectively (Rubin, 2007). Continuous monitoring of the region shows that recent eruptions have been shifting towards the east, from a new vent. This new vent is called the Kupaianaha and it is slowly becoming exposed on the Earth’s surface.J.
Tuzo Wilson proposed a hypothesis to explain why the Hawaiian Ridge is unusually placed at the center of the Pacific plate, rather than on a tectonic boundary: this is known as the “hotspot theory” (Okubo et al, 1997). Wilson theorized that its linear geography was due to the movement of the Pacific plate (seen from right to left in Figure 1), which is shifted by an immobile flume of hotter magma within the Earth (Okubo et al, 1997). As the rocky crust of the volcano is pushed over and the seafloor spreads along the plate boundary, the temperature of the localized hot spot melts the Pacific plate above the hot spot (Zerkel, 2014). The magma that is produced by the melting rock of the Pacific plate rises through the mantle and the crust as a thin thermal plume. Eventually, the thermal plume forms an active seamount beneath the ocean and causes it to increase in height until it reaches the ocean surface and becomes an island volcano (Zerkel, 2014). The island then pushes away from the hotspot, as the Pacific plate moves northward, and room is made for a new island to form on top of the hotspot (Perez, 1999). A zone of magma formation is present here, known as the fixed “hot spot”, which is the source of the volcano.
Kilauea The Kilauea Volcano is located on the southern end of the island of Hawaii and is the most active of Hawaii’s five volcanoes (Heliker et al, 2004). In the Hawaiian language, its name means “much spreading” or “spewing”, a reference to its continual outpouring of lava (Perez, 1999). The Kilauea volcano is around 4,200 feet elevation, with a circular caldera at least a 525 feet deep (Perez, 1999). This ancient volcano is a shield volcano and it appeared over sea level more than 100,000 years ago: it is estimated to be around 400,000 to 600,000 years old (Perez, 1999). This unique volcano mainly produces basaltic lava but is periodically known to explode (Perez, 1999). Over the past century, the volcano has been dormant for only the 18 years between 1934 and 1952 (Hill, 2014). In 1790, the volcano had an eruption that killed at least 80 native Hawaiians, whose footprints can now be viewed in the Hawaii Volcanoes National Park (Bagley, 2014).
Kilauea has had, and will continue to have, a considerable impact on both the landforms and the human populations in the surrounding area. Of the 45 serious eruptions of Kilauea in the twentieth century (Zerkel, 2014), the Pu`u `O`o Eruption, Kilauea’s most recent and ongoing eruption, began in January 1983 (Zerkel, 2014). According to the U.
S. Geological Survey (USGS), in this cycle there have been more than sixty recorded eruptions. The 1983 eruption has produced at least 0.
5 cubic miles of lava, covering almost 40 square miles of landscape and adding 0.8 square miles to Kilauea’s southern shore (USGS, 2017). The eruptions of the Kilauea volcano have substantially altered the terrain, making it difficult to traverse on foot or in a vehicle, and have fatally affected many lives in the area.In March of 1990, Kilauea was recorded that year to be experiencing the most devastating eruption interval in modern history (Mattox et al, 1993). Lava flow made its way through Kalapana and its town before reaching the ocean in 1986 (Mattox et al, 1993).
As a geographical consequence of the eruption, the 82 foot wall of lava demolished 181 houses and resurfaced up to eight miles of highway. The unexpected explosion at the time of eruption also destroyed the Royal Gardens subdivision, the Hawaii Volcanoes National Park visitor center, and more than 200 other structures in the town of Kalapana (Zerkel, 2014). Despite the great risk and dangers, Kilauea seems to remain a popular tourist attraction.
A broad cloud of deadly gas and pale smoke still frequently smothers the small town of Pahala near the Volcano, which has severely impacted the townspeople’s crops and health (Bagley, 2014). In 2009, the gas being released was so toxic that parts of the island have been declared a disaster area. Many of the island residents from nearby towns were notified to “not wait for an alert if they feel ill from the volcanic output” and it has essentially become completely uninhabitable (Rubin, 2013). Figure 2: Eruption at Kilauea destroys homes and communities in Kalapana (Photos: Rubin, 2013)Figure 3: Highways buried under a lava flow in Kalapana, Hawaii (Photo: Pleasance, 2014) Figure 4: USGS map of lava flow hazard zones, Hawaii, based on expected eruption sites (Pleasance, 2014) Kilauea is differentiated from its sister volcanoes by its form: it is a shield volcano.
Shield volcanoes are among the largest volcanoes on Earth, and have active flowing lava, which at the point of eruption is 1,292 to 2,192 Farenheit (Bagley, 2014). The gentle slopes at the summit are produced by basaltic lava flows (Bagley, 2014), which flows for very long distances – incinerating anything in its path – before cooling and solidifying. The geographic landscapes and the ecological community of the island of Kilauea are continually reformed and threatened by the volcano. Lava flows have suppressed most of the sandy terrain in the vicinity. Flowing lava has ignited forests and ash from explosive eruptions suffocates the local plant life (Hill, 2014). Rainfall near Kilauea’s southwestern rift zone mixes with volcanic sulphur dioxide, resulting in acid rain (Hill, 2014) that kills plant life in the region (Perez, 1999). Although there are not immediate and critical threats to local communities, the surface flow remains active.
Local officials have cautioned visitors and residents to avoid the beach by Kamokuna, after discovering a fresh lava flow entering the ocean there.Figure 5: Pu’u’O’o vent, the source of current eruptive activity; and Healemm’uma’u, one of two active vents on the crater (Pleasance, 2014) ConclusionsThe volcanoes of Hawaii occur over a natural hot spot: their eruptions will never cease. The Hawaiian hot spots are thought to have been active for at least 70 million years, and, as an active volcano in the modern day, Kilauea may erupt at any given moment. This shield volcano shows frequent eruptions and outbreaks from the summit. The eruptions of volcanoes like Kilauea demonstrate the unique power that nature has to shape landforms and geography in a dramatic way. Volcanoes create dramatic scenery and beautiful displays of erupting lava, but can also have damaging consequences for ecosystems and people living nearby. Continual survey and monitoring of the volcanoes of Hawaii is essential to mitigate hazards and manage the ever-present dangers for those living in the shadow of the volcano.