Origin of the Hawaiian Islands

Mauna Kea from the west, Nov 2015.

From a geologic perspective, Hawaii is an ephemeral and dynamic anomaly. The islands’ origins lie deep undersea where a large hotspot feeds a succession of active volcanoes underneath the center of the Pacific plate. Measured against geologic history, each island lives a very short life - they burst forth from the sea floor and then quickly drown under the forces of erosion.

Hawaiian volcanoes are the largest on earth, by height (as measured from the sea floor) and by total mass. In fact, their mass is so great that they depress the Earth’s crust in their vicinity. Whereas the typical depth of the seafloor might be 4.5 km, near Maui and the Big Island, the volcanic giants push sea floor depths to over 9 km.

The arc of the Hawaiian Islands formed as a result of the northwest-ward movement of the Pacific plate, currently estimated at a rate of 10 cm per year. New volcanoes form over the hotspot with great rapidity, taking only about 0.3 million years between their inception and the point at which they break the ocean surface. The Big Island is the youngest in the Hawaiian chain, with the oldest rocks dated to about 0.6 million years. Oahu formed about 3-4 mya, and Kaua’i and Ni’ihau have the oldest rocks at about 6 million years old.

The Hawaiian archipelago. Map from Langenbeim and Clague (1987).

To the northwest of the main Hawaiian Islands lies a series of atolls (including Kure and Midway), which are volcanic islands in their old age, hanging on to the sea surface by their reef building corals. Farther into the north Pacific, the Hawaiian Island chain bends northward and becomes the Emperor Seamounts which stretch towards Russia. The bend in the path is dated to about 43 mya, and the change in course of the Pacific plate is believed to be linked to the collision of the Indian subcontinent with Asia at that time. 

Topography of the Big Island, Hawaii, with elevations in feet. Mauna
Kea (north) and Mauna Loa (south) both exceed 13,000 ft elevation.
Map modified from USGS, "Ground Water Atlas of the United
States. Source.

Hawaiian volcanoes progress through 4 stages, starting with the preshield phase when volcanic activity begins. Stage 2 is the shield stage and is the most active period of volcanic activity when the vast majority of the volcano’s volume is created. Magma rises from the hotspot located as deep as 60-70 below the crust where it is stored in shallow reservoirs. During volcano growth, erupting lava emerges both from the summit of the volcano and from several lateral rift zones. The post-shield stage is next, and consists of additional volcanic activity for about 0.1 to 0.3 million years after the shield stage. Finally, after perhaps a quiescent period, there is the rejuvenated stage, a period of variable length where some additional volcanic activity may occur. The Big Island is the only Island in the shield stage. Landslides and erosion gradually wear down the volcanoes.

There are five volcanoes comprising the Big Island: Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea. Only the latter two have erupted recently. Kilauea is the most active volcano in the world. I hope to see lava flows when we visit the National Park in a few days. A bit to the southeast of the Big Island lies the submerged Loihi, which is the newest volcano in the long Hawaiian chain. Some thousands of years into the future, it may form its own island by breaking the ocean surface or it may merge with its neighbors to grow the size of the Big Island.

The five volcanoes of the Big Island. Map and key modified from Sherrod et al. (2007).

References

Clague DA, Dalrymple GB. 1987. The Hawaiian-Emperor Volcanic Chain. Part I. Geologic Evolution. USGS Professional Paper 1350.

Langenbeim VAM, Clague DA. 1987. The Hawaiian-Emperor Volcanic Chain. Part II. Stratigraphic Framework of Volcanic Rocks of the Hawaiian Islands. USGS Professional Paper 1350.

Sherrod DR. 2009. Hawaiian Islands, Geology. In: Encyclopedia of Islands, Gillespie RG and Clague DA (eds), University of California Press, Berkeley, CA, p.404-410.

Sherrod DR, Sinton JM, Watkins SE, Brunt KM. 2007. Geologic Map of the State of Hawai’i. USGS Open-File Report 2007-1089.