I joined the Hawaiian Trail and Mountain Club (HTMC) to climb the summit of Koko Crater on the Ka Iwi Coast of East Oahu which has unusual geological features found no where else on the island.

Originally named “Kohelepelepe” meaning “traveling vagina” in Hawaiian, Koko Crater is the 1,208 foot volcanic cone over Hawaii Kai with an opening on one side — hence, its name.  According to legend, the crater was created in this shape during Pele’s epic battle with Kamapua’a, the pig demigod.


Koko Crater is one of a chain of volcanic tuff cones along the Ka Iwi coast which were created when magma came into contact with sea water.  The crater is made from layer upon layer of consolidated volcanic ash with different erosional properties.  Some of the softer light colored layers have eroded away leaving the harder darker colored layers on top completely intact.  Overhanging rock formations on the lip of the crater rim — visible in the above photo — and arches on the ridges of the mountain are the result of these erosional differences between layers.


Our hike route started in the gully across the highway from the sandy cove at Halona Point.  Hikers must climb up multiple layers of tuff to gain the top of the rocky ridge and then follow the ridge up as it climbs to the rim of the crater.


The top of the ridge is dominated by low-lying coastal plants such as ilima, nehe and this native morning glory, pa’u-o-hi’iaka (Jacquemontia ovalifolia) which produces delicate lavender-colored flowers no more than half-an-inch across.


Due to Kona winter storms over the past six weeks, Koko Crater and the Ka Iwi Coast received considerable rainfall which has turned the vegetation green.  In the summer months when rain is scarce, the landscape turns from green to yellow to golden-brown.


The ridgeline leads up and over an amazing natural arch.  The light beige colored layer of tuff is softer and has eroded away leaving the dark brown layer on top completely intact.  The long narrow hole over which the arch passes is about 10 feet high and 60 feet long and is oriented at an angle of about 30 degrees.


The exhilarating climb over the steep arch was made much easier by the installation of several straps and ropes — many thanks to Jim Yuen (in dark blue shirt) and Ralph Valentino (in light blue shirt) who arrived early to install them over the entire length of the arch.


While the rock arch is steep it is actually climbable without ropes.  A series of steps have been chipped onto the surface of the rock to create footholds.


Richard Bailey sits on the edge to photograph hikers as they make the heart-pounding climb over the arch.  Hikers who have previously cleared the arch continue onwards on the ridgeline to reach the crater rim.


While climbing up the steep slopes I came across native iwaiwa ferns (Doryopteris decora) which grow in cracks between the rocks where moisture collects.


After climbing up another several hundred feet up the mountain we reach the edge of Koko Crater.  Tom Mendes, current president of HTMC, greets hikers as they reach the rim.


One of the native plants growing along the rim of the crater is ma’oli’oli (Schiedea globosa) which is common along drier trails like Makapu’u TomTom and Puu Manamana.


Hikers make their way along the narrow rim of the crater towards Puu Mai, the summit of Koko Crater, upon which sits the remains of an old World War II bunker.


The summit of Koko Crater, at 1,208 feet elevation, provides this view of Hanauma Bay, Hawaii Kai and Mauna Leahi (Diamond Head) and a 360 degree panoramic view of the surrounding area.


While exploring a rocky outcrop near the summit, I stumbled upon a rarely seen endemic Hawaiian amber snail or pupu kuahiwi in Hawaiian (Succinea caduca) about a quarter inch long crawling in a patch of orange and white lichen.  According to snail expert Daniel Chung, these snails cover themselves with dirt and other material and are extremely difficult to find.  Had it not been for the rain storm earlier in the morning which made the snail to venture out onto the brightly colored lichen, I probably would not have seen this creature.  These well camouflaged snails eat decaying vegetation and live in the drier parts of the island where they survive dry periods by sealing themselves in their shells.


After lingering at the summit for a while, I convince a handful of hikers to explore the Hawaii Kai facing rim of the crater which is knife-edged at several locations and tricky to cross. Barbara, August, Jill, and Kaiomi make their way across the narrow rim as low-lying clouds hang over Hawaii Kai.


For the most part the crater rim is not difficult to circumnavigate but there are several tricky spots where balance and coordination are paramount. After crossing a few dicey spots we turn around to return to the summit of Koko Crater.


After returning to Puu Mai — the summit of Koko Crater — we descended the railway tracks that were built to service and supply the bunker at the top.   The tracks are the most direct route to 1,208 foot summit.


After making our way through the firing range we crossed under the highway through a tunnel and made our way along a ledge on the coast where the footings of Koko Crater meet the ocean.  The multiple layers of tuff (consolidated volcanic ash) create interesting geological formations at this eroded gully spanned by a bridge along the coastline.


The hike along the sea ledge is always a fun adventure but hikers must remain vigilant for rogue waves at all times.  Back in 1922, a large wave swept two hikers off the ledge and claimed the life of one, during an HTMC hike across sea ledges on the Ka Iwi Coast.


Kaiomi waits her turn as Jill climbs a series of ropes to climb up to the road.  Several of us choose to forgo this climb in favor of a nerve-racking dash across the ledge between waves to climb up at a less steep location.


Once we reached the road we made our way back to the charming sandy cove at Halona Point where our cars were parked, and reflected on the exceptional hike we just completed.  The Koko Crater hike is a breathtaking geological adventure over the top of an arch, along the narrow rim of the crater, and across sea ledges along the ocean.


Hawaiian Native Plants – Doryopteris, University of Hawaii, Department of Botany

History of the Hawaiian Trail and Mountain Club from 1910 to 1960, R.J. Baker

Littoral Cones, Rootless Cones and Splatter Cones

Personal Communication with Daniel Chung, Snail Expert, University of Hawaii and Bishop Museum

Personal Communication with John Hall and Kenji Suzuki, Native Plant Enthusiasts

Sites of Oahu, Elspeth P. Sterling and Catherine C. Summers, Bishop Museum Press, 1978, pg 267

Volcanoes in the Sea, The Geology of Hawaii, Gordon A. MacDonald, Agatin T. Abbott, and Frank I. Peterson, University of Hawaii Press, Pg 17