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Among the more interesting walks that may be taken from the Military Camp is that along the rim of Kilauea Caldera. The trail along the rim may be followed either to the right, to the Volcano Observatory, or to the left, to Volcano House and Park Headquarters.
The caldera, commonly but not very correctly called the crater, is the large depression formed by the collapse of the almost flat top of the Kilauea dome. It is a broad depression, 4.5 km across, surrounded by an irregular series of circular faults or cracks and terraces. The camp is on one of these terraces, with a low cliff back of it and the main cliff to the front, a short distance beyond the main highway. This flat is covered by ash and coarser pyroclastlc material (ejected pebbles, cobbles and boulders of lava).
Directly across the highway from the camp the trail leads toward the rim. The vegetation is an open scrub of Styphelia tameiamelae (pukeawe), Vaccinium reticulatum (ohelo), Dodonaea viscose (aalii) and stunted Metrosideros collina var. incana (lehua). The ohelo berries, of a beautiful red color, are edible, through the flavor is not very extraordinary. Care must be taken not to confuse Vaccinium berries with those of Wikstroemia, which are poisonous. Vaccinium may be known by berries crowned by the calyx and containing many small seeds. Wikstroemia has one large seed or stone.
In clumps of bushes the erect fern fronds are Polypodium pellucidum, while the heavy, leathery fern with a thick erect rhizome or short trunk is Sadleria cyatheoides (amaumau). The latter becomes more common nearer the crater rim. Sadleria is the Hawaiian equivalent of the genus Blechnum, found commonly in most other tropical areas. An indication of this relationship that is not often pointed out is the reddish cast of the young fronds, a character found, among ferns, principally in Blechnum and its very close relatives, otherwise only in Adiantum. Sadleria differs in its leathery fronds and in being bipinnate.
In the open spaces between clumps of bushes, where there is ash of a sandy texture, *Bulbostylis capillaris and *Conyza canadensis are abundant.
As the trail reaches the rim, an awesome view presents itself, of a great solidified lake of swirling lava. Wisps of steam arise here and there, and in the middle distance is the gaping pit of Halemaumau, site of much of the eruptive activity of this volcano. The last time lava actually welled up out of the pit and spread over the caldera floor was in 1935. It will be seen that very little vegetation has been able to establish itself on the lava-lake in 26 years. A few tiny tufts of vegetation may be seen here and there.
Examination, even without binoculars, of the rim to right and leŁt, will show sections of the cliff separated by great cracks, ready to fall in and add to the talus that lines the base of the cliff.
Along the rim to the right the vegetation is an irregular scrub, similar to that between the rim and the Military Camp, but with more abundant Sadleria, especially in the cracks to the right. It will be noted that the trail is on a section separated from the crater wall by a great crack. It will eventually fall into the caldera during one of the frequent earthquakes that are felt here.
Here on the right the vine climbing in the trees is Smilax sandwicensis. The coarse tufted green sedge is Machaerina angustifolia and the silvery grass-like plant is Astelia menziesiana, of the Liliaceae. A creeping small-leafed shrub is Coprosma ernodeoides, (kukaenene), and the tangled dichotomous fern is Gleichenia linearis var. tomentosa.
After walking 100 m or so between the cracks and rim it is advisable to take the first opportunity to step across the crack to the right and Join the main travelled trail, 10 m or more from the rim. The vegetation becomes sparser and lower, more in the cracks than on the flat areas between them. Near the edges of the cracks, sheltered by bushes, are tufts of Luzula hawaiensis and Gahnia gahniaeformis. On the open ground are *Bulbostylis, Conyza canadensis, *Hypochaeris radicata, and locally, for a short distance along the trail, *Polypremum procumbens.
After this rather open area, the scrub becomes more luxuriant with larger bushes and small trees. The shrub with broad dull yellowish green leaves is Santalum ellipticum paniculatum (sandalwood). On the right of the trail is a large erect bush of *Myrica faya, an aggressive invader of pastures and open ground introduced from the Azores.
Then the vegetation again becomes lower and more open. *Oenothera stricta (or perhaps O. odorata) is rather common in the openings. The scrub becomes still lower and more open until there -is as much or more open ground as vegetation. Occasional great boulders lie along the trail. They were thrown out by the steam blast in 1924 (or perhaps by the one of 1790).
On a low lava scarp are a few small lehua trees. From the top of this, stretches a flat area with no trees, but with sparse scrub with conspicuous elongate Coprosma ernodeoides. This low desert-like vegetation extends across the small plateau bordering the caldera as far as the Volcano Observatory at Uwekahuma.
Back on the rim opposite Kilauea Military Camp, the trail to the left along the rim runs through an open scrub of Styphelia, Vaccinium, Dodonaea, Sadleria and Polypodium with scattered small Metrosideros (lehua) trees. In the cracks that parallel the rim Sadleria is abundant, and Machaerina angustifolia with its hard long grass-like leaves. A bit away from the rim Gleichenia forms low tangles. The large yellow flowers are *Oenothera stricta, the small ones *Hypochaeris radicata. The small shrub with short lance~oblong leaves in six conspicuous ranks and clusters of small heads of yellow florets is Dubautia ciliolata var. laxiflora. Grasses along this trail are *Andropogon virginium *Sporobolus africanus, *Sacciolepis indicus, and a native tussock-forming species, Deschampsia nubigena Grass-like, also' is *Cyperus Polyanthos. The soft, red, edible ohelo berries (Vaccinium reticulatum) are abundant here. Some variation may be seen here in the Metrosideros collina (lehua) with a bright green-leafed bush on the right, but most of the trees are the common variety incana, which colonizes ash and lava.
As the trail descends a short defile Sphenomeris chinensis, Nephrolepis exaltata, Wikstroemia sp. and Gahnia gahniaeformis may be seen growing together on the left. On the slightly lower level at the bottom of this descent the vegetation is sparser and lichens cover much of the ground. A few meters along are distance and direction signs. Among the weedy grasses along this trail are *Anthoxanthum odoratum (sweet vernal grass) and *Setaria geniculata (yellow foxtail). If the ohelo berries are ripe great variation in size, color, and flavor will be evident.
Just before the trail comes out on the Steaming Flats Gleichenia linearis is abundant on the right with Lycopodium cernuum, the strange little tree-like plant with hanging cones on the tips of its branches and long runners arching between the erect fruiting stems. On the Steaming Flats the vegetation becomes very low and dwarfed. The lehuas, now very widely scattered, are here only about one meter tall, everything else less than half that. The abundant gray moss that shares the bare spots with the lichens is the widespread Rhacomitrium lanuginosum var. incanum, found from Iceland to Hawaii and on Hawaii from sea level to the top of Mauna Loa.
In the first steam crack, on the right, dwarfed Sphenomeris and Nephrolepis may be seen lining the edges. An interesting experiment may be performed here if someone lights a cigarette and blows smoke into the crack, great increase in steam will be seen, due to the nucleation of the super-saturated water vapor. Beyond this, Paspalum orbiculare and *Pityrogramma calomelanos are common. The right hand branch of the trail follows a great steam crack filled with luxuriant Nephrolepis sp., *Axonopus compressus (carpet grass) lines the margin and is abundant on the flat. The small purple flowered herb in the cracks is *Cuphea carthaginensis. Luzula hawaiiensis is also there.
The Steaming Bluff, largely bare of vegetation at the top is Just to the right of the trail. The lava slope below is covered by lehua and Gleichenia. On the flat back of the bluff two orchids, *Spathoglottis plicata and *Arundina bambusifolia may be seen.
Beyond another large steam crack is an intersection offering a choice of three trails. The one to the right, the Sandalwood trail, enters a low open lehua forest with an abundant tangled ground layer of Gleichenia. In the numerous large cracks, ferns are abundant, including Nephrolepis, a gigantic Thelypteris, *Pteris vittata, and *Pityrogramma.
The undergrowth gradually changes, along this trail, from Gleichenia to Sadleria. Wikstroemia and a Coprosma are occasional Around the third bridge *Eupatorium riparium, a serious weed, has gained a foothold. One hundred meters or so beyond this bridge the sandalwood trees (Santalum ellipticum var. paniculatum) for which the trail is named may be fled by their dull yellow-green leaves and, if in bloom, their fragrant greenish very small flowers. Smilax sandwicensis twines over a tree to the right of the trail, and Astelia menziesiana on the ground beneath it. Coprosma ernodeoides forms masses on the ground.
Beyond the Santalum, on the left, the small grass, curiously like a diminutive bamboo in appearance, is Isachne distichophylla, representative of an important Pacific genus. Astelia and Wikstroemia are found here.
This is a fairly well developed lehua forest, representing a stage toward the giant forests to be seen on older lavas. The abundance of Lycopodium, Sadleria, Machaerina and Gleichenia shows that it is still a relatively young forest. It may be noted that as yet there are few Cibotium (tree ferns), though some may be seen farther in the forest to the left. *Paspalum conjugatum (Hilo grass) and *Cyperus polyanthus are weeds in the trail.
The great crack on the left shows that the section of the rim on which the trail runs may sometime fall into the caldera. Lycopodium cernuum is unusually common It was in the steam cracks here at Kilauea that Otto Degener discovered the gametophytes of this species almost 40 years ago.
As the trail descends and goes along a ledge on the cliff the new cinder cone at Kilauea Iki, formed in 1959, may be seen in the distance. Pteridium aquilinum is common here, as well as Andropogon glomeratus and a number of other weedy grasses. *Fragaria is along the trail. From' a shelf away from the cliff, the trail turns left down to the foot of the cliff, where the Halemaumau Trail branches off in taller lehua forest with more Cibotium.
The trail then climbs a scrub-covered cliff to the left. The scrub is of small lehua, Dodonaea viscosa and Santalum. Weedy grasses, *Eupatorium riparium, and *Hypericum japonicum are common. The view of the cliffs, caldera floor and Byron's ledge is spectacular.
A *Hedychium, *Lythrum maritimum, and *Cyperus brevifolius are seen here along the steps cut in the rock. The virgate shrub with still pointed leaves below the huge rock on the right is Hedyotis centranthoides, member of a large tropical genus with a number of very peculiar Hawaiian members. *Fuchsia magellanica hangs over the trail, Cibotium chamissoi (tree fern, hapu) is above a narrow defile, at the upper end of which Cyrtandra cf. cordifolia may be seen.
Up the trail, tall Cibotium lines the path; under it the ground is covered by *Hedychium, *Tritoma crocomaeflora, *Commelina diffuse, and a mat of *Selaginella kraussiana. Toward the top, the lehua forest is lower. Hedyotis glomerata is very common. Hypericum japonicum forms a low herb cover along the trail.
On the level terrace the forest is more open, with scattered Cibotium and tangles of Gleichenia. The trail to the right from the intersection leads by the Volcano House, a fine hotel, with many ornamental plants, both planted and naturalized. The small white flower seen here and there on depressed leafy stems is *Erigeron karvinskianus. The Hawaii National Park Headquarters is across the road from the hotel.
To the left, at first near the road, is the trail back to Kilauea Military Camp. A meadow with sparse planting of young koa saplings has a vegetation completely made up of exotic weed species. *Erigeron karvinskianus, *Commelina diffuse, *Cyperus brevifolia, *Cynodon dactylon, *Cyperus polyanthos, *Cyperus sp., *Paspalum dilatatum, *Desmodium intortum, *Rubus penetrans, *Rosa spp., *Bidens pilosa, *Sacciolepis indica, *Anthoxanthum odoratum, *Hypochaeris radicata, *Pennisetum clandestinum, and *Holcus lanatus are all common. *Tritoma forms great masses, multiplying only vegetatively, as no fertile seeds are found in the capsules. At the end of this meadow are clumps of ornamental *Rhododendron, the beautiful but aggressively weedy *Tibouchina urvilleana, *Mows sp., *Psidium guajava, and a slender bamboo.
From here and along the side road to the Sulphur Banks is an open lehua wood. At first *Tibouchlna and *Hedychium are common, then Gleichenia and abundant Lycopodium cernuum.
Off the road to the left a small trail leads to a row of steaming vents with sulphur deposited on the ground and on plants around them. Across to the right, at the end of the road, is a spectacular deposit of sulphur on a steaming bank practically devoid of vegetation. In front of this is a considerable open flat with a very low vegetation of Gleichenia, Lycopodium, Luzula, *Erechtites' Styphelia, *Arundina' Vaccinium, *Andropogon, Sphenomeris, *Spathoglottis, Gahnia, *Cyperus, Dodonaea, Nephrolepis, *Conyza, *Sacciolepis, and *Waltheria In the center of this, in a basin-shaped depression, there is almost bare ground with Cladonia, Rhacomitrium, and scattered plants of a curious depressed, dwarfed form Of *Fimbristylis dichotoma. The entire vegetation is dwarfed.
At the other end of this opening the trail passes into denser tangles of Gleichenia, tufts of Machaerina, scattered Metrosideros and Coprosma Coprosma ernodeoides. Forest is on the left. Then the trail crosses a strip of lehua forest with abundant Sadleria. On the other side of this is the inner side of the Steaming flats, with similar low vegetation to that in the Sulphur Bank opening. Great steaming cracks are common. Taking the right fork at the intersection, the trail skirts the inner edge of the flat, through Gleichenia tangles along the forest margin. Some areas of the flat to the left are bare except for the gray moss, Rhacomitrium lanuginosum and clumps of *Melinis minutiflora (molasses grass). Here are great erratic lava boulders, probably thrown from Halemaumau, almost 3 km away, by the steam explosion of 1790. In other areas the Gleichenia gives way to low scrub of Vacclnium, Dodonaea, and Styphelia. To the right at the base of a low scarp, the large leafed plant is Cordyline fruticosa. In a weedy area near the foot of this scarp the hairy endemic var. hillebrandii of Cenchrus echinatus may be seen.
The trail climbs the scarp onto another terrace flat, with open low scrub forest of lehua, locally mixed with Dodonaea and Styphelia. Low shrubs are Dubautia and Vaccinium. Pteridium aquilinum, Sadleria, Polypodium pellucidum and various weeds are found.
In grassy openings and lehua savanna are *Oenothera stricta, Gahnia, and scattered Santalum. The trail crosses a sizeable flat of this character and emerges at the Military Camp.