Sulfur Bank

This site is a bit of a paradox.  You can smell the sulfur fumes in the air.  You'd expect the rainfall in this area to be very acidic; you'll not be disappointed.  The few measurements made indicate that from this perspective, it is a harsh environment.  The paradox comes when you look at the plants.  There is an abundance of species and many appear to be thriving, even some quite close to the sulfur vents.

Admittedly, many of the plants are stunted.  That gives a hint that something is limiting the root growth.  As a result, there is more to this environment than just the air -- and rainfall -- quality.  Soil acidity is a likely candidate.  Soil temperature must also be important although only reconnaissance-level measurements have been made (check this link for more information).

Take time to examine the distribution, abundance and general health of the plants in this area and you'll see how well adapted the plants are to this type of environment.  It is clear that we need more environmental measurements if we are to sort out exactly what is happening here.


Elevation is about 4,000 ft.  Rainfall and air temperature will closely match that recorded at HVNP Park Headquarters.

Plant Species Checklist

Click the following links for the type of checklist that you want.

Getting There

The road to Sulfur Banks (spelled "Sulphur Bank") by the National Park Service) is located about 0.2 miles to the south of Park Headquarters along Crater Rim Road.

The sign along the Crater Rim Road (shown below) is near Park Headquarters and points to a short (about 0.1 mile) dead end road.

There is a small parking area at the end of the road.

Sign marking the road to the sulfur bank near Park Headquarters Parking area adjacent to the sulfur bank


There are numerous cracks and crevices in the this area.  It is best to stay on the obvious trails.  Be careful around the steam vents.

The Park asks you to refrain from damaging the soft sulfur crystals.

If there is any standing water, it is likely to be very acidic.

The panoramic view below provides a general overview of this area as seen from the approach road.  The gentle slopes of Mauna Loa are seen in the background.

The sulfur bank is shown on the right, adjacent to the parking area.  There is a trail on the left margin of the flat area.

Panoramic view of the sulfur bank area as you approach

The view from the top of the sulfur banks.  There is a small group of plants just below the banks on the right, adjacent to the bare area.  To the left of the bare area is a relatively lush stand of plants, including several medium-sized Metrosideros polymorpha (Hawaiian: `ohi`a).

Notice the mound of rocks piled adjacent to the parking lot.  These are shown in detail below the panorama.

Panoramic view from the sulfur bank

You can see your first sulfur deposits adjacent to the parking area.  A mound of rocks has been placed over a vent.  The stem that comes out of this vent carries sulfur that is deposited as crystals, shown below.

Vents on the nearby cliff also deposit sulfur but they are much less accessible.

Mound of stones over a sulfur vent adjacent to the parking area

Sulfur crystals in a steam vent next to the parking area

The sulfur bank
There are a number of plants growing close to the vents.  While this seems like an extremely hostile environment (you easily smell the sulfur when you are near a vent), these plants seem to grow quite well, although they are stunted.

The Metrosideros polymorpha (Hawaiian: `ohi`a) is flowering and producing new leaves.  Other plants close to the sulfur bank include Vaccinium reticulatum (Hawaiian: `ohelo) and Styphelia tameiameiae (Hawaiian: pukiawe).

Metrosideros polymorpha growing near the sulfur bank
Styphelia tameiameiae vaccinium reticulatum and Styphelia tameiameiae

Turning around, so your back is to the sulfur bank, you will see a dense row of generally short-stature plants in the foreground, a large grassy area in the middle, and a dense Metrosideros polymorpha (Hawaiian: `ohi`a) in the background.

Panoramic view of the high diversity plant community

When you examine the dense foreground vegetation, you will find that it consists of a mixture with abundant Dicranopteris linearis ferns, Lycopodium cernuum, dwarf Metrosideros polymorpha (Hawaiian: `ohi`a) and some sedges and grasses.

Dicranopteris linearis (Common Name: false staghorn fern; Hawaiian: uluhe) (shown below) is recognized by its pseudo-dichotomous branching. This is a common fern in many low to mid-elevation sites.

Lycopodium cernuum (Common Name: club moss; Hawaiian: wawae`iole) (shown below right) is a club moss found growing both here, in the mid-elevation woodlands and in the upper-elevation rain forests.

The high-diversity sulfur bank plant community
Dicranopteris linearis Lycopodium cernuum
These sedges are common among the plants at the margin of high-diversity. sedge

The opposite side of Sulfur Banks  area (opposite from the steaming cliff) has a vegetation composed primarily of the grass Andropogon virginicus (Common name: broomsedge), with scattered clumps of other plants.

There are a number of active steam vents along the edge of the forest, as well as in the flat areas along the trail.

Two of the forest-margin steam vents are shown below.

A steam vent along the forest edge A steam vent along the forest edge
The Crater Rim trail goes along the edge of this sulfur bank area.  This end of the trail has lots of broomsedge (Andropogon virginicus).  This grass is particularly conspicuous because it remains standing when it is dead.

A closer view of some Andropogon virginicus is shown below.

There are a number of fern growing along the trail edge mixed with the grass.  They include the false staghorn fern (Dicranopteris linearis; Hawaiian: uluhe) and the common swordfern (Nephrolepis exsaltata; Hawaiian: ni`ani`au, `ikupukupu).

Crater Rim trail cutting through the edge of sulfur bank

Andropogon virginicus

The bamboo orchid (Arundina graminifolia) grows in clumps along the trail.  Generally, the plants are seen without flowers, but occasionally you are likely to see one standing with a flower as a relatively  bright marker among the other plants.
Arundia graminifolia Arundia graminifolia
This prolifically fruiting Vaccinium reticulatum (Hawaiian: `ohelo) was found near a steam vent on the flat.

Such steam vents may be an important source of additional moisture for the plants and there is often more diverse set of plants around these vents.  The same is not true for the sulfur vents on the other side of the area; they are not being crowded by plant growth in the same way.

Vaccinium reticulatum
There are a number of bare patches in the flat area.  Some are obviously associated with steam and sulfur vents and the absence of plants is quite obvious.

The substrate (shown below) of some of the bare areas consists of what appears to be blue-green algal mat.  There are lichens growing on some of these pieces.

Sometimes the areas are not completely bare but have just a few short-stature scattered grasses (Andropogon virginicus).

Area with bare ground along side Andropogon virginicus

Blue-green algal mat?

Another relatively bare area with stunted Andropogon virginicus

Field-Trip Questions

How many species can you find growing in this area?  Rank them in terms of general abundance?

What are the major factors that limit the distribution of the plant species in this area?

Acid rain generally has a reputation for harming vegetation; how can you explain the growth of the plants in the immediate vicinity of the sulfur vents and the adjacent Metrosideros polymorpha forest?

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Last Updated: 08/08/00

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