Southward displacement of Kilauea Volcano's east rift zone

The active part of Kilauea's east rift zone is moving southward, as measured geodetically. The part of the rift zone nearest the summit should show more displacement because of the greater frequency of dike injection near the summit magma reservoir. The cross section and map below show schematically the stages in the development of the bend in the upper east rift zone.

Simplified cross section of east rift zone, Kilauea Volcano, Hawai`i

Cross section from Swanson and others (1976).

Each new dike that moves from the summit magma reservoir into the east rift zone accompanies widening of the rift zone. Because the north side of the rift zone is buttressed by the enormous mass of Mauna Loa (not shown), the rift zone is forced to spread primarily southward (right in cross section). This southward spreading results in the progressive southward displacement of the active axis of the rift zone relative to the flank of Mauna Loa. Location of A-B cross section is shown in map below.

When a dike reaches the surface of the rift zone, lava erupts onto the surface and adds another flow to Kilauea. Dike 1 is oldest; and dike 5 is still erupting lava that may eventually cover lava flows from dike 4. In a less schematic diagram, dikes would be so closely spaced that they would define a wedge-shaped prism of higher density than the surrounding lava flows.

Simplified map of summit magma reservoir and east rift zone of Kilauea Volcano, Hawai`i

Simplified map showing possible development of bend in east rift zone of Kilauea Volcano because of the progressive intrusion of dikes along the south side of the east rift zone near the summit reservoir. The size of the reservoir is exaggerated for clarity and the shape is greatly simplified; the summit reservoir is between about 1 and 6 km below the surface. The active dike complex is shown in red; the cooled part of the dike complex is shown in black.

Early stage. Dikes extend eastward from the summit reservoir. The great mass of Mauna Loa volcano (not shown), located north of the reservoir and growing dike complex, effectively "locks" the north side of the growing rift zone. 

Intermediate stage. As the mobile south side of the rift zone moves southward near the summit reservoir to accommodate an increasing number of dikes, the location of dikes moves progressively southward. The dikes remain radial to the reservoir but must curve farther downrift to accommodate themselves to the greater south flank movement.  

Present stage. Bend is accentuated as more radial dikes intrude near the summit area. 

References

Swanson, D.A., Duffield, W.A., and Fiske, R.S., 1976, Displacement of the south flank of Kilauea Volcano: the result of forceful intrusion of magma into the rift zones: U.S. Geological Survey Professional Paper 963, p. 39.