Restless Kilauea

Halemaumau Crater inside Kilauea's caldera.

Kilauea lies on the southeastern slopes of Mauna Loa. One of five volcanoes on the Big Island, it is the most active. The caldera itself is one of the centerpieces of Hawai’i Volcanoes National Park. It is an oval depression, a few miles across, its floor paved with twisted dark grey barren lava. Calderas form as the summit of the volcano collapses. At the west side of the caldera is the steaming depression of Halemaumau, visible only from a distance. During the day steam and sulfurous gases billow up and are blown to the west by the trade winds. At night the basin glows a fiery orange.   

The caldera area is active with steaming vents, and lush forests grow up the slopes of the volcano to the rim. There are many more craters along the slopes of the volcano, some visible from Chain of Craters Road.

Repeated lava flows down the slopes of Kilauea over the decades are recorded in the mosaic of forest and barren rock across the landscape of the Park. The majority of surface rocks on Kilauea are less than 500 years old, making these among the youngest rocks on earth. The lava consists of a variety of forms, from braided twisted rock to large plates that have cracked. The Hawaiian names for two main classes of cooled lava are a’a and pahoehoe. The a’a lava is jagged rubble, lying in heaps on the landscape. The smoother pahoehoe is more common. Until these new deposits erode to form soils, there is little space for plants to colonize.

Kilauea volcano on the Big Island. Map from USGS, Hawaiian Volcano Observatory.

Halemaumau crater glowing at night.

Steaming vents in vegetation on the northern side of the Kilauea caldera. Halemaumau crater is to the left.

Lava flows down Kilauea as seen from Chain of Craters
Rd. The a'a is dark grey; pahoehoe is lighter grey. The
Pacific Ocean is visible in the distance.

Click here for a USGS thermal webcam view into the lava caldron of Halemaumau Crater.

References

Holcomb RT 1987. Eruptive history and long-term behavior of Kilauea Volcano. Chapter 12. USGS Professional Paper 1350.

National Park Service. 2008. Hawai’iVolcanoes National Park Business Plan. 

Ka Lae

The southwestern coast of the Big Island is known as the Kau district. It is sparsely populated and transitions from the forested slopes of south Kona to wind-swept grasslands at the southern tip of the island (Ka Lae) to the volcanic terrain of the National Park farther east.

A wave pounding the southern coast at Kae Lae. Padina and other seaweeds carpeted this great southern tidepool.

Ka Lae.

There is some spectacular coastline at the southern end of the island. A paved road leads from the Belt Highway to Ka Lae, which is the southern-most point in the 50 US states. A rocky shore of black lava is swept hard by the wind and pounded by surf. Tropical seaweeds line the coastal rocks and filled a few tide pools. The overcast sky present over the last few days in south Kona gave way to sun and cumulous clouds at Ka Lae. Looking south, I thought of the thousands of miles of open ocean that stood between this point and the next land to the south, not even knowing which islands would be closest.

Five kilometers to the east of the southern point is Papakolea, a green sand beach, one of only a few in the world. We hiked along the hot, dry, dusty and windy lattice of orange dirt roads that lead from a parking area near Ka Lae to the small cove with the famous green sand. It is a tourist trap of sorts, complete with a small local economy that offers cold drinks to parched hikers and truck/van rides over the rough terrain for those so desiring. Beaches with rugged black lava occurred along the trail. The upland was carpeted in grasses, dancing elegantly in the consistent warm wind.

Volcanic coastline along the route to green sand beach.

Green sand beach and the grey bluffs that form the
east rim of the old volcano.

After an hour or so, we finally reached the cove, an extra wind-swept nook with black lava to the right and a grey striated cliff to the left. At the base of the cove was a short stretch of green sand, comprised of olivine, a light green mineral. The olivine is derived from a 50,000 year old cinder cone that sits right here, a part of one of the rift zones of the massive Mauna Loa volcano to the north. I was swimming in a small relict volcano!

Polished olivine gives the sand its green hue at Papakolea.

References

https://en.wikipedia.org/wiki/Kau,_Hawaii

https://en.wikipedia.org/wiki/Papakolea_Beach

Honaunau Bay

Our first two full days on the Big Island provided a chance for beach exploration on the south Kona coast. To snorkel I originally wanted to visit Kealakekua Bay, a marine life conservation district (state marine reserve), but the only public road led to the southern part of the Bay where the swell was probably too significant for the kids to venture much into the water. Honaunau Bay to the south became an excellent alternate location, and I the reef were enjoyable enough to return for a second day.

Slate pencil urchins, Heterocentrutus mammillatus.

The Bay is located just north of a small National Historic Park and seems to be a popular tourist location. Many bobbing snorkelers notwithstanding, the fringing coral reef that hugs the shore was teeming with biological activity. Most human visitors stayed close to home base and it was easy to get away from the crowds by venturing a bit north just offshore. The reefs gradually descended offshore, to depths of probably at least 50 feet. Bright yellow tangs and many other species were abundant in shallow water, so it was easy to see quite a few fish species in only 10-20 feet deep.

Corals comprising the reefs came in various shapes, mostly as massive plates, and some were bleached. The most abundant motile invertebrates may have been urchins, or at least this was the taxonomic group that caught my eye. Pencil urchins with their brick red cumbersome spines were tucked into crevices in the complex reef, while large black urchins with full arrays of thin quill-like spines ventured out in the open, cognizant that no other reef creatures would be likely to interfere with their activities.

The fish were most impressive, occurring in abundance, busily tending to the business of reef life. Bright yellow tangs, in groups or large schools were probably most common. Other groups included butterfly fishes, flamboyant Moorish idols, triggerfish and parrotfishes. There was some chasing, but much of the activity involved feeding; many species were presumably herbivores grazing the sparse algae that happen to grow up on the reef. I enjoyed the solitary greenish blue parrotfish which tended to be shy when I tried to approach with a camera. Most species stayed close to the reef though a few ventured higher into the water column. Some thin blue fish in contrast, stayed just beneath the water’s surface, and since one tends to look down while snorkeling, it was a while before I noticed them.

A reef fish sampler. Top row, from left: moorish idol, Zanclus cornatus with orange band surgeonfish, Acanthurus olivaceus; unknown white and gold-colored butterfly fish; yellow trumpetfish.  Bottom row, from left: fourspot butterflyfish, Chaetodon quadrimaculatus; whitebar surgeonfish, Acanthurus leucopareius; unidentified parrotfish.

Thin, well camoflauged bluish fish hanging out near the water's surface.

A shallow coral escarpment with a pair of ornate butterfly fish, Chaetodon ornatissimus.

References

Mahaney C, Witte A. 1993. Hawaiian Reef Fish. Blue Kirio Publishing.

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.