NPS Sites along Oceanic Hotspot Tracks
Shaded relief map of United States, highlighting National Park Service sites along Oceanic Hotspot tracks. Letters are abbreviations for NPS sites listed below. Sites in Hawaii and American Samoa formed where the Pacific Plate is moving in a northwestward direction over hot plumes of mantle material rising from deep within the Earth.
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
Oceanic Hotspots
- NPSA—National Park of the American Samoa, American Samoa—[Geodiversity Atlas] [Park Home]
- HALE—Haleakala National Park, Hawaii—[Geodiversity Atlas] [Park Home]
- HAVO—Hawaii Volcanoes National Park, Hawaii—[Geodiversity Atlas] [Park Home]
Oceanic Hotspot
National Park Service sites in Hawaii provide an exceptional glimpse at landscapes developing as a tectonic plate capped by thin oceanic crust moves over a hotspot. Broad, gently sloping shield volcanoes develop on the seafloor as the Pacific Plate moves over the Hawaiian Hotspot. As eruptions continue an island pokes up out of the ocean. Eventually the plate motion carries the island away from the hotspot; volcanism wanes and then stops entirely. The island and surrounding ocean floor sink down as the underlying mantle cools and contracts, and erosion wears away at the island. The Hawaiian Islands thus get progressively smaller and lower as they move away from the hotspot. As time wears on the islands are so low that only coral reefs extend above the sea, until they finally sink completely as a chain of underwater seamounts.
Hawaii—Emperor Hotspot Track
National Geographic Society Physical Globe.
The topography and bathymetry (underwater topography) of the northern Pacific Ocean reflect the movement of the Pacific Plate over the Hawaiian Hotspot. Prior to 42 million years ago, the Pacific Plate was moving northward, forming volcanic islands that are now the Emperor Seamounts. The plate motion has changed to northwestward, forming the Hawaiian Ridge and Hawaiian Islands.
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
The islands get older, lower and smaller as they move away from the hotspot, which is currently located under Hawaii Volcanoes National Park. The submerged Hawaiian Ridge is old volcanoes that formed before the current Hawaiian Islands formed, while Loihi is a new volcano that has not quite risen above the surface of the Pacific Ocean.
In 1916, the same year the National Park Service was formed, Hawaii National Park was established to preserve and showcase the Hawaiian Islands’ volcanic features. In 1961, that large park was separated into Hawaii Volcanoes National Park on the Big Island of Hawaii, and Haleakala National Park on Maui. Hawaii Volcanoes National Park lies directly above the Hawaiian Hotspot and includes portions of two very active volcanoes, Kilauea and Mauna Loa. Haleakala National Park encompasses the summit area of Haleakala Volcano, which has moved off the hotspot but still has some eruptions.
The islands, atolls, and seamounts of the Hawaiian Island – Emperor Seamount Chain illustrate the stages of development as the Pacific Plate moves over the Hawaiian Hotspot. On the southeast, a still-submerged volcano called Loihi represents the initial stage. Hawaii Volcanoes and Haleakala national parks have features that reflect the second and third stages, respectively, as volcanic islands develop over the hotspot and are then transported away by the moving plate. Low-lying atolls and submerged volcanoes along the Hawaiian Ridge and Emperor Seamount Chain represent the two last stages caused by erosion and thermal subsidence some distance from the hotspot.
Evolution of Hawaiian Volcanoes
The Hawaiian Islands—The Emperor Seamount Chain develops as volcanoes form above the Hawaiian Hotspot and then ride away on top of the Pacific Plate. An island emerges as lava erupts on the seafloor (Loihi) and eventually piles up above sea level (Hawaii). After moving over the hotspot, volcanic activity wanes (Maui) and eventually ceases. The island gradually erodes and sinks until all that remains are coral reefs just above sea level (Midway Atoll). Eventually, the island is totally submerged (Koko Seamount).
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
The Hawaiian Islands are only the tips of enormous shield volcanoes. Hawaii Volcanoes National Park on Hawaii lies directly above the hotspot and has high elevations and extensive volcanic activity. Haleakala National Park displays the waning stages of volcanism that occurs on the lower topography of Maui, an island that has recently moved off the hotspot. From there the islands get progressively older, lower and more eroded as volcanic activity ceases.
Hawaiian Island Attributes
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
The Big Island of Hawaii is the most volcanically active place on Earth. Off and on for the past 700,000 years, material has been pouring out, piling flow upon flow onto the growing shield volcanoes. Unlike composite volcanoes, which may erupt sporadically for a few months, Hawaiian shield volcanoes can erupt continuously for years. Kilauea Volcano lies directly above the hotspot and has most of the volcanic activity. Its most recent eruption started in 1983 and, as of 2019, has continued ever since.
Volcanoes on the Big Island of Hawaii
Photo from U. S. Geolgical Survey.
The Big Island called Hawaii has five active volcanoes, including Mauna Loa and Kilauea in Hawaii Volcanoes National Park (HAVO). Recent volcanic eruptions are commonly out of rift zones on the flanks of the volcanoes, such as the Northeast Rift Zone on Mauna Loa and the Southwest and East rift zones on Kilauea.
Modified from “Earth: Portrait of a Planet,” by S. Marshak, 2001, W. W. Norton & Comp., New York.
The large shield volcanoes on Hawaii extend to almost 14,000 feet (4300 meters) above sea level. But the bases of the volcanoes lie about 18,000 feet (5500 meters) below sea level, on the floor of the Pacific Ocean.
Features at Hawaii’s national parks provide intriguing clues about the way magma flows beneath a volcano and eventually reaches the surface. Magma can accumulate in chambers beneath the summit region of a shield volcano. Although summit eruptions occur, more often the magma spreads outward and erupts through long fissures along the flanks of the volcano, known as rift zones. Some of the magma hardens into sheet-like dikes below the surface, or is carried great distances through underground lava tubes before emerging as surface flows. In Hawaii Volcanoes National Park, magma rising in vertical, sheet-like patterns results in fissure eruptions through rift zones out of the flanks of Kilauea and Mauna Loa.
Solid materials commonly expand as they heat up. The increase in volume of mantle material at a hotspot causes the Pacific Ocean floor to elevate as the Pacific Plate moves over the Hawaiian Hotspot. In addition, a huge amount of volcanic material erupts onto the seafloor above the hotspot. The Big Island of Hawaii reaches elevations of nearly 14,000 feet (4,300 meters) above sea level.
Mauna Loa: Tallest Mountain on Earth
Photo by U. S. Geolgical Survey. Graphic modified from “A Dynamic Landscape Formed by the Power of Volcanoes,” by Rebecca H. Ashton, M. S. Thesis, Oregon State University, 2003.
Hawaiian shield volcanoes have enormous height and volume. Mauna Loa (the “Long Mountain”) starts 18,000 feet (5,500 meters) below sea level, and rises to nearly 14,000 feet (4,300 meters) above sea level. From its base on the floor of the Pacific Ocean to its summit on the Big Island of Hawaii, it is about 100 miles (160 kilometers) wide. Mt. Rainier, a composite volcano in the Cascade Mountains of Washington state, is about 14,000 feet tall, but only about 10 miles (16 kilometers) wide.
From one perspective, the Hawaiian Islands contain three of the five tallest mountains on Earth. Hawaiian volcanoes actually start on the ocean floor, some 18,000 feet (5,500 meters) below sea level. On the Big Island of Hawaii, Mauna Kea and Mauna Loa rise 13,796 feet (4,205 meters) and 13,679 feet (4,169 meters) above sea level, respectively. From their bases on the seafloor to their summits on the Big Island, those two mountains are each about 32,000 feet (9,750 meters) tall! The top of the highest point on Earth, Mt. Everest, is only 29,035 feet (8,850 meters) above sea level. Considering sea level as the base of Mt. Everest, then Mauna Kea and Mauna Loa are about 3,000 feet (1,000 meters) taller. Mt. Everest is thereby the third tallest mountain in the world, followed by K-2 at 28,250 feet (8,611 meters). Haleakala, on the island of Maui, extends from 18,000 feet below sea level to 10,023 feet (3,055 meters) above, making it the 5th tallest mountain in the world, about 28,000 feet (8,500 meters) high.
The basaltic lavas in Hawaii are so fluid that they can travel along the flanks of volcanoes, below ground as well as above. Once a hard crust forms over a flow, the lava may be so well insulated that it can remain hot long enough to travel several miles. Lava tubes are an integral part of the plumbing system of a shield volcano, allowing single eruptions to disperse lava over large areas. The most recent eruption of Kilauea that began in 1983 pours out of an opening at Puu Oo. The lava enters a system of lava tubes, through which it flows 7 miles (12 kilometers) downslope, before pouring out into the ocean at Pulama Pali. Older lava tubes can be seen at Hawaii Volcanoes and Haleakala national parks.
Fluid Basalt Eruptions from Hawaii’s Shield Volcanoes
The low-silica content of basalt lava allows it to flow freely, forming cinder cones and lava tubes. Movement of the fluid lava out of rift zones on the flanks of the large shield volcanoes forms lines of spatter cones and vertical dikes.
Hawaii Volcanoes National Park
Fountain eruption during the 1959 eruption of Kilauea Iki.
U. S. Geological Survey photo.
Pu'u O'o is a cinder cone formed by a fountain eruption during the ongoing activity on Kilauea Volcano that began in 1983.
U. S. Geological Survey photo.
View through a collapsed roof (skylight) of red-hot lava flowing through a lava tube during 1969–1974 eruption of Mauna Ulu.
U. S. Geological Survey photo.
Entrance to much older Pua Poo Lava Tube.
Photo by Rebecca Ashton.
Line of spatter cones forming during 1983 eruption of Kilauea Volcano.
U. S. Geological Survey photo.
Haleakala National Park
A vertical dike was once magma that cooled and hardened on the flanks of Haleakala Volcano.
Photo by Robert J. Lillie.
When fluid magma has a lot of gas and the eruption is around a central vent, material may shoot high into the air like a fire hose. The magma cools in the air and rains down as blocks ranging in size from small (ash), to medium (cinders) to large (volcanic bombs). A large pile of such material around the vent builds up into a cinder cone. Liquid magma along rift zones may splash out as blobs of lava, building up as a line of spatter cones. There is often magma left within fissures after eruptions from rift zones cease. That material cools and solidifies into sheet-like bodies known as dikes. Such intrusive rock is often harder and more resistant to erosion than the surrounding volcanic layers, making dikes stand out.
Lava Surfaces
Basaltic lava surfaces can have different textures depending on how the lava cools. Where the lava is hot and free to flow, it forms a smooth, ropy surface, known as pahoehoe (“puh-hoy-hoy”). When the lava flow cools down it becomes more sluggish, forming a surface of broken, jagged blocks called aa (“ah-ah”). Aa flows can be very difficult and dangerous to walk across, tearing boots to shreds.
Hawaii Volcanoes National Park
Pahoehoe lava has a smooth, ropey surface, formed when the lava is very hot and free-flowing.
Photo by Robert J. Lillie.
Haleakala National Park
Aa lava has sharp, angular blocks that develop when the lava is cooler and more sluggish.
Photo by Robert J. Lillie.
Collapse Crater Formation
At times enough magma can flow out of an underground chamber that the ground collapses into the vacated space. Spectacular examples are preserved at several NPS sites (for example, Crater Lake National Park in Oregon). Very young collapse craters on many different scales can be seen in Hawaii Volcanoes National Park. One of the larger features, a caldera at the top of Mauna Loa, is 4 miles (6 kilometers) long and 1½ miles (2½ kilometers) wide. Kilauea summit caldera is about 2 miles (3 kilometers) in diameter; its walls are so steep that they often give way as landslides.
Magma accumulates in a chamber beneath a volcano as lava erupts through the summit and along fissures on the flanks. At times the magma inflates and erupts a large volume of material that partially empties the chamber.
Modified from “Earth: Portrait of a Planet,” by S. Marshak, 2001, W. W. Norton & Comp., New York.
A collapse crater (caldera) develops when the summit region of the volcano collapses as rubble into the emptied-out magma chamber. Lava flows and cinder cones can form during later eruptions on the caldera floor.
Modified from “Earth: Portrait of a Planet,” by S. Marshak, 2001, W. W. Norton & Comp., New York.
Kilauea Volcano in Hawaii Volcanoes National Park has a large caldera on its summit. Smaller collapse craters are found on the floor and flanks of the caldera, including Halemaumau and Kilauea Iki. The Volcano House is an historic national park hotel overlooking Kilauea Caldera. The Hawaiian Volcano Observatory of the U. S. Geological Survey monitors active volcanoes in Hawaii and assesses their hazards.
U. S. Geological Survey photo.
National Park of American Samoa
Hawaii is not the only place where the Pacific Plate is currently riding over a hotspot, or has done so in the past. The floor of the Pacific Ocean is scarred with numerous tracks of islands, coral reefs, and submerged seamounts. The oldest of the tracks are parallel to the northward trend of the Emperor Seamount chain, and the younger ones follow the northwestward line of the Hawaiian Islands. Along one of the tracks is U. S. territory that includes the National Park of American Samoa. Similar to Hawaii, the Samoan Islands consist of interlocking shield volcanoes with basalt lava flows, cinder cones, and collapse calderas. The heavy vegetation, erosion, coral reefs, and old volcanic rocks suggest that the Samoan Islands are between the low island and atoll stages of passage over the Samoan Hotspot.
Tau Island
Seafloor Coral
Ofu and Olosega Islands
The Samoan Islands are forming as the Pacific Plate moves west-northwestward over the Samoan Hotspot.
Photos by Emily Larkin.
Figures Used
Related Links
Site Index & Credits
Plate Tectonics and Our National Parks
- Plate Tectonics—The Unifying Theory of Geology
- Inner Earth Model
- Evidence of Plate Motions
- Types of Plate Boundaries
- Tectonic Settings of NPS Sites—Master List
Teaching Resources—Plate Tectonics
Photos and Multimedia—Plate Tectonics
Geological Monitoring—Plate Tectonics
Plate Tectonics and Our National Parks (2020)
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Text and Illustrations by Robert J. Lillie, Emeritus Professor of Geosciences, Oregon State University [E-mail]
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Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute.
Last updated: February 11, 2020