Where Did Hawaii Come From?

The Hawaiian Islands have long captured people’s imaginations with their rugged volcanic landscapes, world-famous beaches, and vibrant culture. But where exactly did these islands in the middle of the Pacific Ocean come from?

If you’re short on time, here’s a quick answer: The Hawaiian Islands were formed by volcanic hotspots underneath Earth’s moving tectonic plates over millions of years, first emerging from the sea as small islands that later combined into larger landmasses.

In this article, we will discuss the fascinating geological history behind the formation of the Hawaiian archipelago. We’ll cover topics like plate tectonics, mantle plumes, and types of volcanic eruptions that contributed to building up the islands we know today.

Plate Tectonics and the Movement of the Pacific Plate

The Theory of Plate Tectonics

The theory of plate tectonics explains that Earth’s outer shell is divided into multiple plates that glide over the mantle. As these plates move, they collide, spread apart, or slide past each other. This causes earthquakes, volcanoes, oceanic trenches, and mountain building.

The Pacific Plate is the largest tectonic plate, covering about 103 million square kilometers.

According to the plate tectonics theory proposed in the 1960s, Earth’s lithosphere, which includes the crust and upper mantle, is made up of a series of rigid plates that float on the solid yet flowing asthenosphere layer below.

These plates move very slowly, at about the same rate fingernails grow, driven by convection currents within the mantle.

Movement of the Pacific Plate over the Hawaiian Hotspot

The Pacific Plate has been moving in a northwesterly direction for over 80 million years. This steady movement has caused the plate to move over fixed hotspots in the mantle below, one of which is located below the current Hawaiian Islands.

This Hawaiian hotspot is an area where hot mantle rock from deep in the Earth melts, becomes less dense, and wells up in plumes toward the surface. Some of this basaltic magma squeezes through weakness in the Pacific seafloor, creating underwater volcanoes.

With the Pacific Plate’s northwesterly drift, the oldest Hawaiian volcanoes are at the northwest end of the island chain, while the southeast end hosts the youngest islands with active volcanoes.

Scientists have used radiometric dating of samples from the islands to determine the ages of the volcanoes. The ages increase progressively along the chain to the northwest. For example, Kauai is over 5 million years old, Oahu is 3 million years old, Maui is 1.3 million years old, and the Big Island of Hawaii is less than 0.7 million years old with active lava flows today.

This age pattern matches what would be expected from a fixed hotspot in the mantle being passed over by a moving tectonic plate. As the Pacific Plate slides over this hotspot at about 8.2 cm per year, it has created the Hawaiian-Emperor seamount chain over 70 million years.

Models suggest this hotspot could continue fueling volcanic eruptions on the Big Island for at least the next 500,000 years before the movement of the Pacific seafloor carries it away from the hotspot.

The Hawaiian Hotspot and Mantle Plumes

What Are Mantle Plumes?

Mantle plumes are columns of hot, molten rock that rise from deep within the Earth’s mantle. As the plumes reach the base of the lithosphere, the rigid outer shell of the Earth, they flatten out and can create large volcanic regions known as hotspots.

Scientists believe mantle plumes originate from the boundary between the Earth’s core and mantle, over 1,800 miles (2,900 km) below the surface. Temperatures in this lowermost part of the mantle allow rock to be partially molten.

Buoyancy causes this less dense molten rock to rise through the solid mantle for thousands of miles until it reaches the lithosphere.

The Hawaiian Islands chain is the classic example of volcanoes formed by a stationary mantle plume. As the Pacific tectonic plate has moved northwest over the Hawaiian hotspot at a rate of around 1 inch (3 cm) per year, the plume has punched through the plate about 100 times over the past 70 million years.

This has created a string of volcanic islands and undersea mounts.

The Hawaiian Hotspot

The Hawaiian hotspot is a volcanic region thousands of miles across beneath the Pacific Ocean. Its exact origin deep in the mantle is debated, but scientists agree the plume is fixed and taps into a vast pool of hot rock, driving surface volcanism as the Pacific plate drifts overhead.

Researchers estimate the plume rises over 1,800 miles (2,900 km) from near the core-mantle boundary to the base of the Pacific lithosphere. Seismic imaging reveals a narrow stem around 400 miles (650 km) wide extending to a depth of at least 1,500 miles (2,500 km), then a bulbous head spreading out like an umbrella under Hawaii.

This gigantic plume head may interact with ancient subducted slabs in the lower mantle and other deep mantle upwellings. However, the clear track of age-progressive volcanoes produced as the Pacific plate moves northwest points to a fixed, long-lived source centered under Hawaii.

The buoyant mantle rock ascending in the Hawaiian plume incubates near the pressure-release zone under the lithosphere before erupting onto the seafloor. Here it ponds and melts into magma, rising into the overlying Pacific plate to feed persistent volcanic activity.

The burning question is – where did such an immense upwelling come from, and what does its existence tell us about the unseen depths of our dynamic planet?

Origins of the Main Hawaiian Islands

Kauai and Niihau

The oldest of the main Hawaiian islands, Kauai and Niihau first emerged from the Pacific Ocean around 5 million years ago. Born of volcanic eruptions from the same hotspot under the ocean crust that continues to give birth to the archipelago today, Kauai rose up as lava poured from vents on the seafloor and slowly built up over eruptions spanning around 2 million years.

The island displays the erosional remnants of lava flows, volcanic ash and breccia from its shield-volcano origins.

Oahu

The island of Oahu began forming as an independent shield volcano around 3 million years ago. A series of lava flows built up the bulk of the island during its main shield-building stage over the course of about 500,000 years.

Oahu displays the classic shape of a shield volcano, with gentle slopes built up by fluid basalt lava flows emanating from a summit vent. The eruption of the Honolulu Volcanic Series around 2 million years ago further added to the island’s size and shape before volcanic activity ceased around 1 million years ago.

Maui and Molokai

The islands of Maui and Molokai share an origin story, joined together as one landmass with the volcanic birth of Maui around 2 million years ago. Maui’s shield-building eruptions contributed over 80% of the volume of these islands over a course of approximately 1 to 1.3 million years.

As volcanic activity waned around 500,000 years ago, erosion and subsidence of the land divided them into separate islands. Molokai displays the deeply eroded remnants of lava flows and volcanic structures from its history attached to Maui. The last eruption on Maui occurred around 50,000 years ago.

The Big Island of Hawaii

The youngest island in the chain, the Big Island of Hawaii is still growing thanks to its active volcanoes including Mauna Loa and Kilauea. Formed over the same hotspot in the mantle plume that gave birth to the rest of Hawaii, the island commenced formation around 500,000 years ago.

Hawaii’s active lava flows and volcanic features showcase the ongoing process of island building from continuous eruptions. With fresh lava rock still cooling from eruptions as recently as 2018, the island continues to expand its land area over new and well-documented lava flow fields.

Eruption Types that Built Hawaii

Shield Volcanoes

The Hawaiian islands were primarily built up over millions of years by fluid basaltic lava erupting from the Earth’s mantle through vents or fissures, piling up over time to form gently sloping shield volcanoes.

According to the U.S. Geological Survey (USGS), shield volcanoes make up the bulk of the Hawaiian island chain, built up steadily by eruption after eruption of highly fluid lava flows that can spread many miles from their vents (1).

Mauna Loa and Kilauea on Hawaii island are classic examples of active shield volcanoes. Their lava moves in channels rather than explode skyward, steadily adding layers to the volcano over time to create a rounded dome-like shape resembling a warrior’s shield.

Cinder Cones

Unlike shield volcanoes, violent eruptions of lava skyward along with volcanic gases and rocky debris construct cinder cones. Cinder cones are smaller and steeper than shield volcanoes, ranging from 300 to 1,000 feet tall with slopes of 26° to 35° degrees.

As the USGS describes, they are built from solidified lava fragments and poorly sorted material known as volcanic cinders or scoria that collect around the vent (2). Some of Hawaii’s famous black sand beaches originated from eroded cinder cones.

While less massive than shield volcanoes, cinder cones add striking dimension to Hawaii’s landscapes, especially on Maui and Lanai.

Rift Zones

Extending outward from the summit and upper slopes of Hawaii’s massive shield volcanoes are networks of fractures known as rift zones from which lava emerges. As tectonic forces stretch the volcanoes over hundreds of thousands of years, long parallel cracks penetrate deep into their structures.

When magma travels up from the mantle into the rift zones seeking escape, it either erupts onto the surface in curtains of fire known as “fire fountains,” or intrudes below ground to construct underground tunnels of magma called lava tubes.

Kilauea and Mauna Loa volcanoes sport two opposing rift zones responsible for many of Hawaii island’s recent lava flows, including Kilauea’s destructive 2018 lower Puna eruption.

Conclusion

The Hawaiian Islands showcase a unique geology that continues to reshape and reform the landscapes. Understanding the volcanic origins of Hawaii gives us an appreciation for the powerful natural processes that built these islands in the middle of the Pacific, creating the beautiful and diverse landscapes we enjoy today.

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