Dr Trevor and Chris Watts (UK)
This is the second of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units.
|A word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.|
Down the Chain of Craters Road
0.3 miles: the July 1974 flow
This flow, which was mostly pahoehoe lava, covered several hectares. It came from the nearby cone of Ma’una Ulu, a subsidiary cone of Kilauea. The eruption began in May 1969 and lasted until July 1974. It featured many periods of spectacular fire fountains, including one that reached 300m high on 30 December 1969 (Fig. 1).
Spreading as far as the sea, it added 94 hectares of new land to Big Island – more than 230 hectares. In addition to spreading across the surface, much lava sank, returning into the ground through sink (‘drain’ or ‘submergence’) craters, such as Alai Crater.
This eruption also featured a considerable amount of ground-fissuring (Fig. 3), although many very broad cracks were subsequently filled by advancing lava. The present lava surface displays much evidence of disturbed, re-worked and broken surface crust, weathering, vegetation regrowth and encroachment from surrounding areas that survived the eruption (Fig. 4).
0.4 miles: Lua Manu Pit Crater
This crater (Fig. 4) was formed in October 1974, when a large fissure opened and almost immediately found itself being filled with flowing lava, which continually drained away down other fissures nearby.
Pit craters are also known as ‘collapse craters’. They are usually formed when the lava still flowing under the crusted surface drains away and the surface collapses. This can result in a small collapse pit – or a huge one 90m across and 45m deep, such as this one. If the under-surface lava continues to flow for some time – perhaps several years – it might repeatedly fill the pit, drain away and be refilled. Characteristically, these craters have sharp sides, and the surrounding area of the rim is clean and bare: no ash, pumice or other debris has been erupted to form a raised rim. That is, they are not the sites of eruptions.
0.4 miles: cinder cones
At the same stop-off, there are two small, well defined cinder cones. These are miniature volcanoes, made of loose fragments of pyroclastic material – ash, cinder and clinker – and were probably formed in a few days, in a ‘one-off’ eruption. These are points where a gas-powered eruption burst explosively up through the lava crust and sent near-solidified material flying – though not too far. They are not known to have erupted from separate fissures and are thus sometimes known as ‘rootless cones’.
The cinder chunks are black, highly vesicular (bubble-filled) basalt, which has been turned rusty red by the intrusion of steam during and after the eruption, causing iron-staining. One cone is cut through by the road, giving a good view of its amorphous structure (Fig. 5). Around it, the 1974 flow stretches into the distance.
1.0 miles: Puhimau Crater
One of the largest collapse craters in the region, Puhimau (‘Poo-ee-mah-oo’) is oval-shaped, and more than 150m deep. It is thought to have been formed when the surface fell into a voided magma chamber below, between 500 and 200 years ago. It has never been flooded by incoming or up-welling lava. The floor is thus the original fallen surface from far above, although it is slowly being buried as fragments break off the cliffs and form scree slopes.
The sides are near-vertical cliff faces and the guard rails are token affairs; and it is possible to walk all the way round the crater – as is the case at most of these craters. It is, however, dangerous, as there are many deep and wide cracks and fissures, which are often half-hidden by vegetation. The northern face, opposite the access point from the road, is home to a number of steam vents that originate among the innumerable truncated lava flows that form the cliff. These vents are often sufficiently strong to cloud the crater in mist, as can be seen in Fig. 6, where the far wall is partly shrouded in vapour.
1.1 miles: the steam vents area
This is a large open meadow of deep grassland and low scrub surrounded by trees (Figs. 7 to 10). It is about 1.6km across, of which 16 hectares are an active thermal area, geologically known as the ‘Puhimau Hot Spot’. It began in the mid-1930s, in response to a rising intrusion within Kilauea’s Eastern Rift Zone.
It is possible to explore all over this space (when it isn’t closed for extermination of ‘little fire ants’). After the first few hundred yards, the grass is punctuated by rising clouds of steam. This is when visitors need to be a little more careful, as these steam vents become more numerous. There is no danger from the usual carbon dioxide and sulphur dioxide fumes, as the steam has de-gassed before reaching this area. These vents are caused by ground water seeping down to the magma below and heating up sufficiently to create steam. The ground just a few metres below is hot enough to kill tree roots, but the shallower-rooted grasses survive, leaving the dead, white-boled trees scattered across the area. Some very extensive patches have been scorched and killed in the past, and are left as white, mineral-crusted areas of bare earth. These can give way underfoot and may still be hot beneath.
Across the area, activity such as this tends to migrate beneath the surface and so there are many abandoned fissures and holes where activity has ceased, at least for the time being. Equally, there are places where new activity is beginning, and the trees and grasses are dying. Some vents have surfaced around trees, perhaps finding a route upwards along root-created cracks. Although many of the steam vents are small – perhaps forming a pit less than a metre across and deep – others are more than 6m across and can be very deep – ‘bottomless cracks’. Others hiss from horizontal ‘caves’ beneath the crusted lava surfaces, and the steam may have weakened the ground, speeding up the weathering and creating deep pits close by.
1.5 miles: Ko’oko’olau Crater
This is a large, steeply-sided collapse crater, approximately 150m across, although it’s hardly possible to tell, as it is completely overgrown with deep vegetation, principally Koa and ‘Ōhi’a trees. There has been no thermal activity of any kind for at least 200 years, hence the dense forest. The name comes from the yellow-flowered ko’oko’olau plant, which also grows here. It is used to make a herbal tea and various medicinal potions, and is a cleansing agent. However, it takes longer to read the text on the packets of tea than it does to observe this crater from the observation point – there is very little to see (Fig. 11).
2.2 miles: Hilina Pali Road
Built between 1933 and 1942, this road snakes 12 miles across the fissures and flows of the Eastern Rift Zone. Hilina means ‘Windy Cliff’. It provides good views of the coast, cliffs and the flows, but there has been little activity here for over 600 years and thus is moderately overgrown. The only activity here is along the ten-mile reverse fault that parallels part of the road. It is still spreading apart by around 5cm a year. It is a reverse fault because the land slipped downwards on the higher part of the slope, so the scarp cliff is facing inland. There is a campsite about halfway along the road and a shelter at the end.
2.3 miles: Devil’s Throat Crater
Although little visited, this is the most impressive of the collapse craters in this region, said by the USGS to be the best example of a collapse crater in the world.
The lay-by is unmade and unmarked, but Devil’s Throat is well worth the stop. There is a dusty trail walk of around 165 feet through patchy, prickly undergrowth and across multiple fissures (Fig. 12) to the edge of the crater.
The rim is completely unguarded by any fencing and is constantly crumbling away (Figs. 13 to 16). This is a place to be very careful. If you feel inclined, it takes about an hour’s careful navigation to hike around the rim – but not too close to the edge.
Devil’s Throat is located between two faults – ‘Bean’s’ and ‘Patty’s’ – which feature numerous fissures and cracks en echelon. These faults are still active and periodically disrupt the surface of the Chain of Craters Road. They have also severely ruptured the ground all around the crater.
The pit began as a small crack, discovered around 1912, little different from any other ground split in the locality. Being on a trail, horse-riders would frequently jump over the fissure, with no idea of its depth. Although expanding, it was only taken seriously in 1921 when it was surveyed by geologists. At that time, it was around 75m deep and the walls were originally overhanging. That in itself was an indication of probable collapse into a magma chamber and there are also indications of stoping, which is the break-up and removal of country rock by rising magma (Fig. 17).
The walls are still actively disintegrating and collapsing, and are now ‘merely’ vertical. The loss of the higher faces has increased the diameter of the pit to 45m. The fallen rocks are filling the pit, and it is now ‘only’ about 50m deep, so it is still deeper than it is wide. A large lava tube that was visible in the north wall has now been buried, along with two smaller ones nearer the bottom. It is presumed that the magma drained out through other, lower ones, which were buried before the pit was discovered.
2.4 miles: two cinder cones
The road goes straight between these two cones, which are larger than the earlier one at 4 miles. The material is semi-cemented ash and cinder, creating cones about 60m long in the line of the road and 7.5m high, although partly excavated for road construction. They are moderately over-grown with small trees, and there is a small, degraded crater at the top of one, from which the pyroclastic material was expelled (Fig. 18).
2.6 miles: Hi’iaka Crater
This collapse crater (named for a sister of the goddess Pele) has existed for several hundred years. It was well-forested, when, in 1968, it was overtaken by an area-wide Kilauea eruption. Ground-swelling, followed by a series of minor earthquakes, culminated in a lava eruption from a fissure inside the crater at 6:00am on 22 August (our wedding anniversary). This swiftly developed into a strong eruption, which fountained to heights of 45m and formed a solidifying lava pool around 18m deep. Other vents opened beneath the lake and on the crater walls, spurting lava. Violent gas emissions followed and then other fountains, with the lake growing to almost 30m deep before it began to crust over, becoming partly covered by incoming lava flows from the side vents, and finally draining away and lowering the surface to around 15m deep. It was all over by lunchtime.
The active centres of the Kilauea eruption migrated away, along the Eastern Rift Zone, and the lava level subsided by another 6m. It is still there (Fig. 19). This was most notable at the time for being the smallest known eruption of Kilauea, and for the vast number of minor ground cracks – including nine across the Chain of Craters Road.
What’s to be seen now is a shallow, tree-covered depression (Fig. 20). We have never gone down to the lava lake because: (a) the undergrowth is very dense; (b) the view is described as ‘uninteresting’; (c) there are glimpses of it from the rim that confirm the ‘uninteresting’ opinion; and (d) there are plenty of other things to look at in this location.
In the next article, we continue our road trip to more craters, lava fields and lava tree forests…
|Almost all the photographs were taken by one of us – Trevor or Chris – except the few that are credited separately. These are available as Public Domain Images from the United States Geological Service (USGS), particularly the Hawaiian Volcanoes Observatory. Innumerable Internet sites provided background information, such as dimensions of craters. The USGS is invariably helpful in answering specific queries and providing access to wider sources. Their weekly publication, ‘Volcano Watch’, is invaluable for general information as well as updates on theories, eruption activity, and trail and road closures and re-openings.|
About the authors
Trevor and Chris are keen amateur geologists living near Nottingham, England. They have climbed many volcanoes throughout the world. Sharing the exploration, photography and writing, they have had numerous articles published on the subjects of volcanoes and their other geological interest – dinosaur footprints (including in this magazine). Now retired from her work as a teacher and head teacher, Chris paints in watercolours, silks and pastels, mostly animal portraits and flowers. Trevor, formerly a teacher, headteacher and school inspector, now writes short stories and poetry for competitions, publication and the mental challenge.