Southwest Rift Zone

This is a harsh environment and only a few plant species are found here. The location is just downwind from Kilauea crater.  The species that grow here appear to do quite well, showing periods of active growth and reproduction.  One of these species is Silene hawaiiensis, a protected species because it is designated as a Federally Threatened Species.

This site allows an inspection of some of the adaptations that plants have to cope with a stressful environment.

Environment

The Southwest Rift Zone is shown in this picture taken at the Hawaii Volcano Observatory.  You can see Halema`uma`u on the left.  The rift zone is on the flat plain just to the right of the small `ohi`a tree in the foreground. The last major activity in Halema`uma`u was in 1967-68, with smaller amounts in 1981. This deposited lots of ash, cinders and stones in the nearby area, including the region of the southwest rift zone. The southwest rift zone is one of two major fracture zones on Kilauea.  The other is the east rift zone; it is the one that is currently most active.

Halema`uma`u emits gasses, like hydrogen sulfide, that combine with water to make the rainfall in this region very acidic.  Measurements as low as pH 2 have been made.

The Southwest Rift Zone area is drier than areas to the north-east since it is several miles away from the crest of the slope up from Hilo.

This is a windy area where protection is afforded only in the depressions created by the rift-zone cracks.

Getting There

Map Blast! Map

There is a small parking area adjacent to the sign marking the Southwest Rift. The area to be visited is behind the cars, to the left. (A link at the bottom of this page to the North-East side of the road examines the right side of the Crater Rim Road.

Warnings

• Be careful to not disturb and of the plants in this area.

This area will be described by looking at two types of habitats, the flat area (below left) and the crack (below right)

Southwest Rift Zone Flat Areas

Coprosma ernodeoides (Hawaiian: kukaenene) is an infrequently found plant sprawling across the flat areas.
Metrosideros polymorpha (Hawaiian: `ohi`a) grows as a few scattered individuals in this area.  Some of the plants show red leaves, perhaps as a result of acid rain.
There are two primary species found on the flat area: Vaccinium reticulatum (Hawaiian: `ohelo) and Silene hawaiiensis. Vaccinium is a low-growing shrub that is widely distributed through the park. Here the plants are generally very short, some being only a foot or less tall. Although the plants are small, they generally have abundant fruit.
Sometimes the fruits are distinctly yellow.
Silene hawaiiensis is also a low growing shrub in this area. The plant has a large tap root. Stems branch from the end of this root.  New growth extends from the tip of stems. Plants often have what appear as dead stems.
This photo shows what appears to be a recent growth spurt.
The flowers are small and tubular.

Rift Zone Cracks

This is a relatively small, shallow crack in the rift zone area.  Even so, it harbors a number of plants along its sides.
Dodonea viscosa (Hawaiian: `a`ali`i) commonly grows as small individuals in the cracks.
You can find the common swordfern (Nephrolepis exsaltata; Hawaiian: ni`ani`au, `ikupukupu) here and there on the sides of some of the cracks.
This small sedge is often found in the cracks.
Styphelia tameiameiae (Hawaiian: pukiawe) doesn't appear to be common in the cracks, but there are a few individuals here.
This grass was seen only once in this area, at the end of a long crack.  It appeared that there was some drainage of water to the place this grass was found.

Useful Links

• The Silene Population on the North-East Side of the Crater Rim Road

Field-Trip Questions

• The Hawaiian Goose, the Nene, is often found in this area. How would you establish if it is eating the plants or their fruits?
• How would you determine if the Silene plant population is increasing, decreasing or staying the same size?
• What is the functional role of the large tap root on the Silene plants?
• What factors might make a difference in the types of plants, and their growth characteristics, found on the flat versus those in the cracks?
• What are the characteristics of the substrate in this area?

References

• Stone, Charles and Linda W. Pratt, 1994, Hawai`i's Plants and Animals: Biological Sketches of Hawaii Volcanoes National Park, Hawaii Natural History Association, National Park Service and University of Hawaii Cooperative National Park Resources Studies Unit.

Outstanding Tasks

• Pictures of the rift crack plants.
• Map of the area.
• Environmental data.
• Links to other Silene information.