Puhimau Hot Spot

This is another of the Park's most challenging environments for plant growth.

The surrounding area is a mid-elevation woodland.



This area was once a mid-elevation woodland, dominated by large `ohi`a trees.  In the winter of 1937-1938, there was a magma intrusion just below the surface (Stone and Pratt 1994: 169).  While this event didn't result in an eruption, it has heated the ground enough to kill all of the trees.  It permits the growth of only the most heat tolerant species, generally those that have only the must superficial root systems.

You can observe the general effects of the heating from the Chain of Craters highway.  The subsurface heating continues to move.  In the last few years the situation has changed so that trees that formed about a 25 meter border that blocked the view from the highway have now died.  You can now see dead and dying trees on both sides of the highway.

Getting There

Drive down the Chain of Craters Highway 1.3 miles from the intersection with the Crater Rim Road.  You will be turning right on an unmarked dirt road just before a cattle crossing.

The top left picture (below) shows the location of the entrance road.  You can see the quality of the road and the general environment in the top right picture.  Go slowly down this rough, narrow road.

The road continues about 0.1 miles, eventually ending in a small parking area.  The road is blocked by several large boulders at this point.

Puhimau hotspot region
Turnoff from the Chain of Craters Highway Road leading to the parking area
Road leading to the parking area Parking area


This is a very sensitive area for several reasons.  Before visiting this site, make sure that you have a legitimate reason for going there and be highly alert to interfering with Hawaiian cultural values.

The Surrounding Forest

Spend some time looking at the plants in the mid-elevation woodland before you enter the hot spot.

There are several individuals of the native sedge Machaerina angustifolia (Hawaiian: `uki) adjacent to the parking area.

In the parking area you will see several species of grass.

Shown below (left) is the flowering head of the bushy beardgrass (Schizachyrium condensatum). 

This is a mixed stand that includes the molasses grass (Melinis minutiflora) (below right)


Machaerina angustifolia
Schizachyrium condensatum Melinis minutifolia
The surrounding forest is a mixture primarily of Metrosideros polymorpha (Hawaiian: `ohi`a) and Myrica faya.

Myrica faya (Common Name: firetree, firebush, faya tree) can be recognized by its conical shape when it grows in this open woodland area.

The firetree is a relatively recent introduction that has become one of the Park's worst pests.  It is thought to have been brought to Hawaii in the 1920s (Lamoureux 1996: 42), although it wasn't until 1961 that it was first seen in the Park (Stone and Pratt 1990: 132).  It is obvious that this fast-growing species is a fierce competitor. This is due, in part, to its being a  nitrogen-fixer. This allows it to make very effective use of the relatively recent lava substrates in this area.

Myrica faya
Look at the trees to see how effectively they shade the forest floor.  This inhibits the growth of understory plants, leading eventually to dense stands of this one species.

The flowers and fruits are small.  Several birds eat the seeds and carry them to other parts of the park.

Myrica faya Myrica faya
Some of the Metrosideros polymorpha (Hawaiian: `ohi`a) have clusters of aerial roots. Metrosideros polymorpha aerial roots
The bamboo orchid (Arundina graminifolia) occurs around the parking area and along the trail. Arudina graminifolia
If you look carefully off the trail near the side of the surrounding forest trees, you might spot a Rubus argutus, the alien blackberry (Hawaiian: `ohelo `ele`ele).
Rubus Rubus

On the Hot Spot

The woodland forest turns into a margin of matted Dicranopteris linearis (Common Name: false staghorn fern; Hawaiian: uhule).

The trail itself is lined with bushy beardgrass (Schizachyrium condensatum).

In the background, you can see some of the larger steam vents near the forest edge on the opposite side of the hot spot area.

Schizachyrium and Dicranopteris on the hot spot margin
Once you are actually on the hotspot, the vegetation is reduced to low-growing forms, punctuated by an occasional Metrosideros polymorpha (Hawaiian: `ohi`a) remnant stump.  These stumps are a reminder that this was once a woodland forest.

All of these stumps are now small vents as the channels once occupied by roots become easy conduits for steam to leave the earth.

Many of the stumps have epiphytic Metrosideros polymorpha growing on them.  Although stunted, these small trees appear otherwise healthy.

The areas of the stump subjected to steam venting get a heavy layer of blue-green algae.  Remember that these cyanobacteria come in many colors.

Hot spot area with a Metrosideros stump
Metrosideros polymorpha growing as epiphytes Blue-green algae in a vent on a Metrosideros polymorpha stump
The endangered species found on this site is Portulaca sclerocarpa (Hawaiian: `ihi makole, po`e).  The general habitat of this plant is shown on the right where there are several dozen individuals growing in and around a slight depression.

Below, the prostrate plant can be seen on the slightly undulating substrate.

Individual plants are found in open areas.

Watch where you walk so that you don't step on a plant!

Portulaca sclerocarpa habitat

Several Portulaca sclerocarpa individuals

Portulaca sclerocarpa
The identification character that separates this Portulaca from the other, more abundant and widespread species, is the white flower.  This picture shows a not-yet-open flower. Portulaca sclerocarpa flower
Portulaca pilosa (Hawaiian: `ihi) is much more common (very abundant and with a widespread distribution through the entire hot spot area) creeping succulent.

This species has small pink flowers.

You'll encounter this species as soon as you enter the hot spot area and find it scattered through out.

Portulaca pilosa
The substrate is worth examining.  There are areas with patches that appear to be blue-green algal blocks.

Many of the plants appear to be rooted in these mats, rather than the soil.


"Blue-green algal" mat
Grass growing rooted on the mat Grass growing rooted on the mat
There are several steam vents on the far-side of the hot-spot area, near the forest margin.

These are easy to spot since they produce copious amounts of steam.

These vents are surrounded by a carpet of mosses and ferns.

Steam vent
As you return from the hot spot to the mid-elevation forest on your way back to the parking lot, notice that the trail is lined with bushy beardgrass (Schizachyrium condensatum).  This is a reminder that invasive weeds often follow trails and that people are one of the dispersal agents.

The adjacent dense forest reduces the light levels enough to inhibit the growth of the grass.

Schizachyrium condensatum lining trail to the woodland

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Last Updated: 07/31/02

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