Rainmaker Mountain (also known as Mount Pioa and Mount Peiva) is the name of a mountain located near

Pago Pago, American Samoa Pago Pago ( or ; Samoan: )Harris, Ann G. and Esther Tuttle (2004). ''Geology of National Parks''. Kendall Hunt. Page 604. . is the capital of American Samoa. It is in Maoputasi County on Tutuila, the main island of American Samoa. Pago Pago ...

Tutuila Island Tutuila is the largest and most populous island of American Samoa and is part of the archipelago of the Samoan Islands. It is the third largest island in the Samoan Islands chain of the Pacific Ocean, Central Pacific. It is located roughly north ...

. Rainmaker Mountain traps rain clouds and gives Pago Pago the highest annual rainfall of any harbor. The average annual rainfall on the mountain is around . It has a three-pronged summit. Rainmaker Mountain and its base were designated a

National Natural Landmark The National Natural Landmarks (NNL) Program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only national natural areas program that identifies and recognizes the best e ...

in 1972 due to the slopes’ tropical vegetation. Rainmaker Mountain is one of several giant volcanic mountains that created Tutuila Island. It dominates the scene from nearly every point in

Pago Pago Harbor Pago Pago Harbor on Tutuila Island in American Samoa is one of the world's largest natural harbors. The capital, Pago Pago, is located on the inner reaches of the harbor, close to its northwesternmost point. It has the highest annual rainfall o ...

. It comprises three mountain peaks: North Pioa, South Pioa, and Sinapioa. The peaks range in elevation from to . The designated landmark area occurs above the contour line. Several endemic species are present only here and on

Matafao Peak Matafao Peak (Samoan: ''Fa’asi’usi’uga o Matafao'') is a mountain in American Samoa, on the island of Tutuila. With an elevation of , it is the highest peak on Tutuila Island. The mountain, like Rainmaker Mountain across Pago Pago Harbor, ...

, the highest point on Tutuila. Rainmaker Mountain, famous in Samoan legend and lore, is also geologically important as an example of a volcanic plug (quartz trachyte). The upper slopes are

montane rainforest Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial f ...

and the crest is montane scrub. It is a volcanic feature known as a

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...

plug, a volcanic intrusion made of extrusive

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

s having alkali feldspar and minor mafic minerals as the main components and a fine-grained, generally

porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...

texture. A closeup of the mountain is visible up Rainmaker Pass. It is located behind the village of Lauli’i on the east side of Pago Pago Bay.

Rainmaker Hotel Rainmaker Hotel was a 250-room luxury hotel in Utulei, Pago Pago, American Samoa. It was the only proper hotel in American Samoa and was operated by the government. The hotel was at its peak in the 1960s and 1970s, when it was known as the Pacifi ...

was a hotel at the port entrance under the mountain. The_Rainmaker_from_near_the_former_Rainmaker_Hotel_-_panoramio

Geology

Rainmaker Mountain is a prominent

dome located near Lauliʻi. It is a quartz trachyte dome measuring approximately 300 meters in width, 720 meters in length, and reaching a height of 515 meters. Its unique structure is a testament to the volcanic history of the Pago Pago area. The mountain is characterized by its composition, which includes

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

that is low in

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, as well as zones in contact with basaltic flows. The dome is primarily formed from basaltic fragments and explosion breccias, with occasional inclusions of trachyte or rhyolite blocks. It is classified as an

endogenous Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell. For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...

dome, which formed through the upward push of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

into a narrow vent roughly 1.25 miles (2 kilometers) in diameter. The volcanic processes that shaped Rainmaker Mountain were intense. The dome rose rapidly, spewing red, white, and black

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

along with

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

-rich cinders. This explosive activity, combined with outbursts of older basaltic materials, created a distinctive montane landscape. The summit features a cratered pumice cone, which formed when pasty lava erupted and partially filled the area.

Columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar join ...

is a noticeable feature, forming at right angles during the cooling phase of the lava. Rainmaker Mountain's formation is closely tied to the evolutionary stages of the Pago Volcano. The tuffs and breccias seen in other parts of the Pago Pago Harbor suggest that similar processes created other trachyte plugs in the region.

Flora

Rainmaker Mountain is home to rare plant species that have been documented only once or twice within the

Samoan Islands The Samoan Islands () are an archipelago covering in the central Pacific Ocean, South Pacific, forming part of Polynesia and of the wider region of Oceania. Political geography, Administratively, the archipelago comprises all of the Samoa, Indep ...

. These include Zschaemum cf. byrone, a grass species, and Mapania vitiensis, a sedge, both of which were found in the montane scrub habitat of the mountain. Additionally, the fern Dipteris, characterized by leaves that resemble those of Tacca, is another rare species recorded in the region. In the Samoan Islands, Dipteris has been observed exclusively on Rainmaker Mountain and Matafoa Mountain, highlighting the ecological significance of these National Natural Landmarks.

Fauna

Petrel Petrels are tube-nosed seabirds in the phylogenetic order Procellariiformes. Description Petrels are a monophyletic group of marine seabirds, sharing a characteristic of a nostril arrangement that results in the name "tubenoses". Petrels enco ...

s and

shearwater Shearwaters are medium-sized long-winged seabirds in the petrel family Procellariidae. They have a global marine distribution, but are most common in temperate and cold waters, and are pelagic outside the breeding season. Description These tube ...

s are known to breed predominantly on the higher elevations of Tutuila, with Rainmaker Mountain serving as a particularly significant habitat. These seabirds are rarely observed near the coastline. Rainmaker Mountain is a nesting site for both the

Wedge-tailed Shearwater The wedge-tailed shearwater (''Ardenna pacifica'') is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a muttonbird, like the sooty shearwater of New Zealand and ...

and the White-throated Storm Petrel. The Wedge-tailed Shearwater, a rare species in American Samoa, likely burrows in the mountain's high-altitude soil. It is also thought to inhabit the cliffs and inaccessible montane scrub of the mountain. In 2023, a groundbreaking discovery was reported: researchers from Archipelago Research and Conservation (ARC), in collaboration with USFWS, DMWR, and NPS, identified four active burrows of the rare Tahiti Petrel on Rainmaker Mountain and Matafao Mountain. This marked the first confirmed breeding activity of the species on Tutuila in nearly 40 years. Additionally, researchers documented new colonies of the Tropical Shearwater.https://www.samoanews.com/local-news/research-team-discovers-rare-seabird-nests-tutuila

References

* https://web.archive.org/web/20061005005025/http://www2.nature.nps.gov/geology/parks/npsa/index.cfm

External links

National Park Service site for Rainmaker Mountain
Mountains of American Samoa Tutuila National Natural Landmarks in American Samoa Volcanoes of American Samoa Volcanic plugs of the United States {{AmericanSamoa-geo-stub

Geology

Flora

Fauna

See also

References

External links