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The Hawaiian Islands rising from the Pacific Ocean showcase perhaps the most quintessential shield volcanoes in the world. If you’re wondering what exactly makes the Hawaiian Islands a prime illustration of these very gently sloping volcanoes, read on below for a deep dive.
Hawaii’s volcanoes are characterized by their broad, dome-shaped structures built up over time by highly fluid lava flows that spread out widely over the land compared to more explosive volcanoes. This ultimately creates the iconic long, wide shape reminiscent of a warrior’s shield that gives shield volcanoes their name.
In this article, we’ll explore the step-by-step geological processes that built the Hawaiian Islands into textbook examples of shield volcanoes. You’ll learn about the specific conditions that lead to their formation, evidence of Hawaiian volcanoes’ historic lava flow and eruption activity that shaped them over millennia, and how the Big Island’s volcanoes represent continuing growth of the Hawaiian Island chain.
How the Hawaiian Hot Spot Drives the Island Chain’s Ongoing Volcanism
The fixed hot spot continually supplies magma
The Hawaiian Islands owe their existence to a fixed hot spot deep beneath the Pacific Ocean crust. This stationary plume of hot rock, located nearly 1,900 miles (3,100 km) northwest of the Island of Hawaiʻi, has persisted for at least 80 million years.
As the Pacific tectonic plate drifts over the Hawaiian hot spot at a rate of approximately 32 miles (51 km) per million years, the upwelling magma punctures the crust and creates volcanoes. The progressively northwestward islands track the ancient movements of the plate.
The hot spot delivers basaltic lava to the surface at a temperature near 2,200°F (1,200°C). This fluid rock material flows easily to form gently sloping shield volcanoes, characterized by volumes of fluid lava flows compared to violent eruptions of ash or debris.
The Pacific Plate drifts northwest above the hot spot
The newest Hawaiian Island, the Island of Hawaiʻi, currently sits above the hot spot. The volcanoes of Mauna Loa and Kilauea exemplify active shield volcanoes, with frequent effusive eruptions. As the Pacific Plate moves, the Island of Hawaiʻi will eventually drift off the hot spot.
To the northwest, the progressively older and inactive islands follow. Scientists utilize radiometric dating to determine each island’s age—the Island of Hawaiʻi is less than 1 million years old, while iconic Kauai tops the chain at 5.1 million years old.
As the islands leave the hot spot, erosion wears down the shield volcanoes. Eventually only their eroded remnant coral atolls remain, ephemeral pinpricks dotting the vast Pacific Ocean.
| Island Name | Age (millions of years) |
| Hawaiʻi | Less than 1 |
| Maui | 1.3 |
| Oʻahu | 3.7 |
| Kauaʻi | 5.1 |
The ongoing drift of the Pacific Plate across the fixed Hawaiian mantle plume demonstrates plate tectonic theory elegantly. As the plate moves northwest at 4 inches (10 cm) per year, so progresses the chain of volcanic islands and seamounts.
To learn more about Hawaiian volcanoes and plate tectonics, check out the U.S. Geological Survey’s Hawaiian Volcano Observatory.
Fluid Basalt Lava Produces Broad, Shield Shaped Volcanoes
Hot spot magma has unique properties
The Hawaiian Islands are located over a fixed mantle plume, an upwelling of abnormally hot rock from deep within the Earth. This creates a volcanic hot spot as magma melts through the oceanic crust. The magma originating from the hot spot has unique properties compared to other volcanic regions.
The Hawaiian hot spot magma is very hot, fluid, and low in silica and gas content. This allows it to flow rapidly in lava channels rather than plugging the volcano’s vent. The chemical composition produces quick-moving basalt lava flows that can travel many miles from their originating vent.
High eruption rates build wide dome structures
The Hawaiian volcanoes have frequent eruptions of fluid lava over hundreds of thousands of years. While stratovolcanoes like Mt. St. Helens may only have one or two eruptions per century, Hawaiian shield volcanoes see near constant activity.
Frequent lava flows piling on top of one another leads to the gradual build up of wide, dome-like structures. Over time, they take on a distinctive shield profile unlike the steep cone shapes of composite volcanoes.
For example, Mauna Loa (“Long Mountain” in Hawaiian) rises 9 km from the seafloor, yet has slopes of only 5–9 degrees. This makes it the largest shield volcano and mountain on Earth.
| Shield Volcano | Stratovolcano |
| Low, broad structures | Steep conical structures |
| Fluid basalt lava | Viscous andesitic lava |
| Frequent eruptions | Periodic eruptions |
| Rare explosive activity | Common explosive activity |
This table compares some of the key differences between Hawaiian shield volcanoes formed by hot spot magma and stratovolcanoes like those in the Cascades volcanic chain.
To learn more, check out these great resources from the USGS Hawaiian Volcano Observatory and Hawaiʻi Volcanoes National Park.
Ongoing Growth of the Big Island and Future Islands
Kilauea and Mauna Loa showcase Hawaiian volcanism in action
The Hawaiian Islands are the archetypal example of shield volcanoes, with two of the most active volcanoes in the world – Kilauea and Mauna Loa – continuing to expand the Big Island (Hawaii island). Kilauea has been near-continuously erupting since 1983, adding nearly 500 acres of new land to Hawaii over the past few decades alone.
Its 2018 violent eruption was a vivid showcase of the raw power of these volcanoes, destroying over 700 homes but also creating nearly 1 cubic kilometer of new land.
Mauna Loa is the largest volcano on Earth, rising 13,679 ft above sea level and extending 18,000 ft below the water’s surface. Though quieter than Kilauea in recent years, geologists consider Mauna Loa certain to erupt again based on past patterns.
Its 1950 eruption sent lava flows 15 miles to the ocean in under 3 hours – a sobering example of how quickly Hawaii’s volcanism can transform landscapes. And with 35-40% of its historical eruptions sending lava toward Hilo, the Big Island’s most populous area, Mauna Loa poses a more direct volcanic threat to residents than Kilauea.
Loihi Seamount will eventually emerge from the sea
The Hawaiian-Emperor seamount chain stretches over 3,600 miles northwest across the Pacific Ocean, with the Loihi seamount representing the next Hawaiian island in the making. Located 22 miles southeast of Hawaii island, Loihi rises 13,796 ft from the ocean floor, with its summit around 3,200 ft below sea level today.
But with an estimated eruption rate 100 times faster than Mauna Loa, Loihi continues to grow – scientists estimate it will break the ocean’s surface in 10,000-100,000 years to form a new Hawaiian island.
As the newest Hawaiian volcano, Loihi provides a unique porthole into the early formation and development of these unique volcanoes. Since its discovery in 1952, decades of research has unveiled fascinating insights into its geology – two intersecting rift zones, frequent submarine eruptions, hydrothermal vents with unique extremophilic bacteria, and more.
While Loihi may now lie dormant preparing for its next eruption, this emerging Hawaiian island remains a compelling showcase of Earth’s ongoing volcanism.
Conclusion
The Hawaiian Islands exemplify shield volcanoes formed through consistent eruptions from the Hawaii hot spot punching through Earth’s crust underneath the slowly drifting Pacific tectonic plate. Their iconic long, broad shape built from fluid lava flows directly results from the unique properties of the hot spot magma together with extremely high historical eruption rates.
Hawaii remains a hot bed of volcanism, with the Big Island’s Kilauea and Mauna Loa continuing to add layers to the Hawaiian chain through frequent eruptions. And a future island is already developing underwater as Loihi Seamount grows on the ocean floor until someday emerging as the newest Hawaiian island.
