Kilauea is an active shield volcano, produced by the Hawaiian hot spot and is located on the main Island of Hawaii. It consists of a summit caldera and a rift zone comprised of two sections, the East and the Southwest (see Fig. 2), moving away from one another.
Figure 1: Google Map of the Kilauea Rift Zone and surrounding features, located on the main island of Hawaii, USA.
Figure 2: Geologic map of the area, including both sections of the Kilauea Rift Zone. Image found in the Bulletin of Volcanology (Moore, R.).
East Rift zone
The East portion of the Kilauea Rift Zone extends eastward, from the summit caldera, for 125km (Moore, R.). This length includes 75km of underwater trace, where it reaches the seafloor (5). The Kilauea volcano's summit is located on the side of Hawaii's Mauna Loa volcano, at an elevation of 522km (Moore, R.) and as it makes its way downslope, it is observed on the surface as a wide ridge (5). The theolitic basalts making up the surface layer are approximately 400 years old, with some exposed lava remnants that date back to 2500 years ago (5).
Recently, this active site has experienced around 100 eruptions (Moore, R.) and the first one to ever occur here is estimated at half a million years ago, before it had ever reached the island rock (4). Along the caldera, past eruptions have left volcanic debris, such as cones and tuffs (Moore, R.), along the slope, as it descends to the sea. The reason for why the outpouring of lava flows, both aa and pahoehoe (4), moves South-East is due to the presence of the large mass of Mauna Loa. It comes into contact with this Kilauea volcano along the North side, and stops the movement of rock or intrusions in that direction, as seen in Figure 3. This leads to a build up of stress, resulting in parallel faults and largely displaced fissures, with offset on the scale of metres (Moore, R.)
Also seen in Figure 3, are the many dikes which rise up eastwardly (Swanson) from the underlying magma chamber situated below the rift zone (5). They reach metres wide, creating new ones towards the South, the youngest labelled #5 in Figure 3. According to the University of Hawaii Manoa, the Kilauea volcano has one of the greatest heat outputs worldwide, which is due to the high activity of the East Rift Zone (4). With the last eruption in 1961, it "may be overdue for its next [one]" (Moore, R.).
Recently, this active site has experienced around 100 eruptions (Moore, R.) and the first one to ever occur here is estimated at half a million years ago, before it had ever reached the island rock (4). Along the caldera, past eruptions have left volcanic debris, such as cones and tuffs (Moore, R.), along the slope, as it descends to the sea. The reason for why the outpouring of lava flows, both aa and pahoehoe (4), moves South-East is due to the presence of the large mass of Mauna Loa. It comes into contact with this Kilauea volcano along the North side, and stops the movement of rock or intrusions in that direction, as seen in Figure 3. This leads to a build up of stress, resulting in parallel faults and largely displaced fissures, with offset on the scale of metres (Moore, R.)
Also seen in Figure 3, are the many dikes which rise up eastwardly (Swanson) from the underlying magma chamber situated below the rift zone (5). They reach metres wide, creating new ones towards the South, the youngest labelled #5 in Figure 3. According to the University of Hawaii Manoa, the Kilauea volcano has one of the greatest heat outputs worldwide, which is due to the high activity of the East Rift Zone (4). With the last eruption in 1961, it "may be overdue for its next [one]" (Moore, R.).
Figure 3: Diagram of how the intrusions influence the growing volcano slopes of Kilauea at the East Rift Zone, found in Swanson and others (1976). http://hvo.wr.usgs.gov/gallery/kilauea/erz/spreading.html
Southwest Rift zone
The Southwest section of the Kilauea Rift Zone does not lead to any lava eruptions onto the volcano. However, there is still rifting occurring here, with a seaward extension as the southwest side of Kilauea is displaced by sliding and counterclockwise rotation of the crustal rock (Myer, D. et al). Both along the rift zone and at the caldera high seismic activity is found, with many shallow, low intensity earthquakes causing displacement (Myer, D. et al). Due to all the stress concentrated here, many slope failures occur and led to the formation of many faults and consequently the Hilina Slump (6). This slumping action is growing every year, with an outwards stretch of 10cm/year on average, as it heads towards the South coast (6).
Additionally, both InSAR and GPS technologies have been used to measure and track the crustal inflation surrounding the main caldera and surrounding rift zones. The data recorded that over the past decade, inflation has occurred over an area which extends for 12km with a width of 8km (Myer, D. et al). Refer to the figure below to view vectors representing the magnitude and directions of displacement (in terms of velocity).
Additionally, both InSAR and GPS technologies have been used to measure and track the crustal inflation surrounding the main caldera and surrounding rift zones. The data recorded that over the past decade, inflation has occurred over an area which extends for 12km with a width of 8km (Myer, D. et al). Refer to the figure below to view vectors representing the magnitude and directions of displacement (in terms of velocity).
Figure 4: Close up view of the main caldera on Kilauea, with faults outlined in white and velocity vectors for various recent events of uplifting are shown. Image as seen in Journal of Volcanology and Geothermal Research (Myer, D. et al).
Kinematics of kilauea rift zones
Figure 5: Kilauea's magma supply pathway: The magma rises from the hot spot supply and reaches below the surface of Kilauea, where it moves along the rift, rises up to the caldera or pushes through fractures before pouring out onto the surface. Image found at: http://volcanoes.usgs.gov/activity/methods/deformation/tilt/kilauea.php.
There are many contributing factors to the stress experienced by the rift zone at Kilauea. Two of the main ones are the following: magmatic intrusions, especially along the East Rift Zone and seismic activity, emphasized along the Southern rifting system. Additionally, both hydrothermal pressure and volcanic gases lead to buildup of stress within the subsurface layers. Over long periods of time, weathering, erosion and movement of continental loads leads to isostatic rebounding, which effects the entire land mass as a stressor as it becomes imbalanced.
The formation of rifts, and their extensional displacement is characterized by a relationship between stress and faults. There is a "high strain and stress changes in the host rocks" (Troise, C.) which causes slipping along the faults with earthquakes on the order of M>7. In these areas, the primary faulting is at a low angle, or rather they are thrust faults and can be either reverse or normal in orientation, however the former is dominant. Altogether, these properties can be used to "explain the main features of Kilauea [rift zone]" (Troise, C.).
The formation of rifts, and their extensional displacement is characterized by a relationship between stress and faults. There is a "high strain and stress changes in the host rocks" (Troise, C.) which causes slipping along the faults with earthquakes on the order of M>7. In these areas, the primary faulting is at a low angle, or rather they are thrust faults and can be either reverse or normal in orientation, however the former is dominant. Altogether, these properties can be used to "explain the main features of Kilauea [rift zone]" (Troise, C.).
Video: Lava flow at east rift zone (2010)
Video taken by Keith Trego, uploaded by John Langton on March 31, 2010.
Sources:
Peer Reviewed
1: Moore, Richard B. "Volcanic Geology and Eruption Frequency, Lower East Rift Zone of Kilauea Volcano, Hawaii." Bulletin of Volcanology. 54.6 (1992): 475-483. Print.
2: Troise, C. "Stress Changes Associated with Volcanic Sources: Constraints on Kilauea Rift Dynamics." Journal of Volcanology and Geothermal Research. 109 (2001): 191-203. Print.
3: Myer, D, D Sandwell, B Brooks, J Foster, and M Shimada. "Inflation Along Kilauea's Southwest Rift Zone in 2006." Journal of Volcanology and Geothermal Research. 177.2 (2008): 418-424. Print.
Web- Others
4: http://hvo.wr.usgs.gov/kilauea/
5: http://hvo.wr.usgs.gov/gallery/kilauea/erz/spreading.html
6: http://www.drgeorgepc.com/VolcanoHawaiiKilaueaInstab.html
Peer Reviewed
1: Moore, Richard B. "Volcanic Geology and Eruption Frequency, Lower East Rift Zone of Kilauea Volcano, Hawaii." Bulletin of Volcanology. 54.6 (1992): 475-483. Print.
2: Troise, C. "Stress Changes Associated with Volcanic Sources: Constraints on Kilauea Rift Dynamics." Journal of Volcanology and Geothermal Research. 109 (2001): 191-203. Print.
3: Myer, D, D Sandwell, B Brooks, J Foster, and M Shimada. "Inflation Along Kilauea's Southwest Rift Zone in 2006." Journal of Volcanology and Geothermal Research. 177.2 (2008): 418-424. Print.
Web- Others
4: http://hvo.wr.usgs.gov/kilauea/
5: http://hvo.wr.usgs.gov/gallery/kilauea/erz/spreading.html
6: http://www.drgeorgepc.com/VolcanoHawaiiKilaueaInstab.html