The Hawaiian-Emperor Chain

The Hawaiian-Emperor Chain

The Tectonic Origins of the Hawaiian Islands

[Illustration: Planet earth showing western hemisphere, Hawaiian Emperor Chain]

 

Picture a jigsaw puzzle on a round ball, with the pieces of the puzzle constantly moving around on the ball’s surface.  That’s a good model of Earth’s geological characteristics.  The ball is Earth, and the puzzle pieces are large sections of the Earth’s crust floating on the molten rock beneath.  These large floating pieces of Earth’s crust are known as tectonic plates.

Earth’s crust is divided up into 12 large tectonic plates along with many smaller tectonic plates.  The Hawaiian Islands are on the Pacific Plate, the largest of Earth’s tectonic plates.

 

Tectonic Plates

All of Earth’s tectonic plates are relatively thin, and beneath them is the molten rock (magma) of Earth’s interior.  These tectonic plates vary from 2 to 75 miles (3 to 121 km) thick.  The plates are thicker under mountains, and thinner under oceans. 

Earth’s tectonic plates are rigid, and tend to drift and slowly move around on the hotter and more fluid mantle beneath them.  This causes the tectonic plates to shift over time, rearranging them on the surface of the Earth.  The Pacific Plate is currently moving northwest at the rate of about 3½ inches (9 cm) per year.

[Illustration: Globe with outline of tectonic plates, Pacific region]

 

The Ring of Fire

Volcanic activity occurs all around the margins of the Pacific Plate, from Japan’s Mt. Fuji, to Mount Pinatubo in the Philippines, to Katmai in Alaska and Washington’s Mount Saint Helens. 

This great circle of volcanoes around the around the circumference of the Pacific Plate has led to the nickname “Ring of Fire,” which describes the volcanic activity.  The boundaries of the Pacific Plate are roughly aligned with the edges of the Pacific Ocean. 

Earth’s tectonic plates are constantly bumping into each other, and these great confrontations cause earthquakes as well as volcanic activity, mostly along the boundaries of the tectonic plates. 

Earth’s major tectonic plates drift at varying speeds and in different directions.  As noted above, the Pacific Plate is the largest of Earth’s tectonic plates, and is currently drifting to the northwest at the rate of about 3½ inches (9 cm) per year.

As the subducted crust of the Pacific Plate melts into the deeper magma beneath the North American Plate, this causes volcanoes to form and erupt back up through the surrounding tectonic plates. 

This is largely how the great mountain ranges of the western United States were formed, and also the cause of the May 18, 1980 eruption of Mount St. Helens in Washington.

The Pacific Plate is also subducting (diving beneath) the other surrounding tectonic plates, such as the Aleutian, and Eurasian tectonic plates. 

[Illustration: Map sketch, Ring of Fire] 

 

Shield Volcanoes, Island Formation, and the Hawaiian Magmatic Hot Spot

Hawaiian volcanoes (known as shield volcanoes) are not produced by a subduction process (one tectonic plate diving beneath another), but instead the Hawaiian volcanoes are produced by a single stationary plume of lava known as the Hawaiian magmatic hot spot.  This plume of lava rises up from deep within Earth’s mantle. 

The Hawaiian hot spot’s lava plume produced all of the Hawaiian Islands as the uprising lava burned through the Earth’s crust and erupted up onto the seafloor forming undersea volcanic mountains.

When a subsea volcano grows tall enough to break the ocean’s surface, the peak becomes an island.  The Hawaiian Islands are the summits of massive volcanoes that grew up from the ocean floor as much as 18,000 feet (5,486 m) below the water’s surface. 

 

Shield Volcanoes

The volcanoes in the Hawaiian Islands are known as shield volcanoes because their broad and even lava flows form a shape similar to a warrior’s shield.

 

Ke one lau‘ena a Kāne.

The rich, fertile land of Kāne.

Puna, Hawai‘i, was said to have been a beautiful, fertile land loved by the god Kāne.  Pele came from Kahiki and changed it into a land of

lava beds, cinder, and rock.

                                                                        (Pukui: 1777: 191)

 

The Hawaiian magmatic hot spot, the deep-Earth lava plume fueling the Hawaiian volcanoes, is about 50 miles (80 km) in diameter.  Currently one edge of the lava plume is under the island of Hawai‘i, fueling the eruptions of Kīlauea Volcano, while the other edge of the magmatic hot spot is about 18 miles (29 km) off the southeast coast of the Big Island, where it fuels the volcanic activity of Lō‘ihi Seamount.

Lō‘ihi is now about 9,000 feet (2,743 m) tall, and the undersea volcano’s summit is about 3,116 fee (950 m) below the ocean’s surface.  Eventually Lō‘ihi will be centered over the uprising lava plume, which is stationary. 

Like the rest of the Hawaiian Islands that came before it, the island of Hawai‘i will be carried away from the hot spot by the northwest movement of the Pacific Plate, making way for the next island to emerge.

One after another, as if on an assembly line, the volcanic islands are produced by the hot spot lava plume.  Each volcanic island forms over the stationary hot spot and then is carried northwest as if on a conveyor belt. 

The Pacific seafloor is moving northwest only a few inches per year, but over millions of years this has resulted in a chain of islands in a line from the northwest to the southeast.  The newest (youngest) islands are at the southeast end of the island chain, while the oldest islands are at the northwest end of the chain.

 

The Hawaiian-Emperor Chain

Over the last 75 to 80 million years, the movement of the Pacific Plate over the Hawaiian magmatic hot spot created a 3,105-mile (4,997-km) long chain of undersea volcanoes known as the Hawaiian-Emperor Chain.  Most of the volcanoes of the Hawaiian-Emperor Chain are completely underwater, and known as seamounts. 

Volcanoes of the chain rising above the water include the 132 islands, reefs, shoals and atolls of the Hawaiian Islands (including the Northwestern Hawaiian Islands).

This line of seamounts and volcanic islands is the result of the 75- to 80-million year history of the Pacific Plate drifting north and then northwest over the magmatic hot spot plume of lava.  This is easily seen when viewing a map of the Pacific seafloor.  The southeastern portion of the Hawaiian-Emperor Chain is called the Hawaiian Island/Seamount Chain, and runs southeast to northwest for about 1,860 miles (2,993 km). 

The upper portion of the Hawaiian-Emperor Chain runs almost due north for about 1,245 miles (2,004 km), and is called the Emperor Seamount Chain.

Together these two sections comprise the Hawaiian-Emperor Chain.  Researchers believe this volcano-building process began longer than 80 million years ago, and the volcanoes from this time have by now moved so far north that they were subducted beneath the North Pacific Aleutian Submarine Trench.

The dogleg in the Hawaiian-Emperor Chain is due to a shift in the direction of movement of the Pacific Plate, from north to northwest, about 40 to 43 million years ago. 

From that time until the present the Pacific Plate has been moving northwest.  The shift in the direction of movement of the massive Pacific Plate from north to northwest was likely due to movements of Earth’s other tectonic plates, particularly the Indian Plate, which collided with Asia resulting in the formation of the Himalayan Mountains.

[Illustration/Graphic: Hawaiian Emperor Chain showing Pacific Plate movement over Hawaiian magmatic hot spot, including seamounts]

 

Above the stationary hot spot lava plume, island after island forms.  One after another each island is carried northwest.  As each island moves away from the active lava plume, it ceases its volcanic eruptions, first becoming dormant and then extinct, and eventually eroding away into the sea. 

This process of island formation and erosion continues today.  At the northwest end of the chain the islands slowly dissolve into the sea, while to the southeast islands continue to grow.

 The Hawaiian Island Chain is just a small part of the Hawaiian-Emperor Chain.  The eight main Hawaiian Islands span over about 350 miles (563 km) of ocean. 

The Northwestern Hawaiian Islands include 124 scattered islets, shoals, and atolls spanning over about 1,050 mi1es (1,690 km) of ocean.  In all, the Hawaiian Islands span over about 1,525 miles, from the island of Hawai‘i at the southeast end, to Kure Atoll to the northwest.

At the southeast end of the Hawaiian-Emperor Chain, islands continue to grow, most notably at the site of Hawai‘i Island’s Kīlauea Volcano, which has been erupting almost continuously since 1983.  The island chain also continues to grow at the site of Lō‘ihi Seamount, about 18 miles (29 km) off the southeast coast of the Big Island.

Lō‘ihi Seamount is very active.  At sometime in the future, perhaps between 50,000 and 200,000 years from now, Lō‘ihi will grow tall enough to break the ocean’s surface and become the next Hawaiian Island. (See Lō‘ihi Seamount section.)

 

Kaua‘i—An Example of the Life of an Island

Because the process of island building is fairly consistent, one may look at any particular island to gain an understanding of how the process works.  The island of Kaua‘i is the northernmost of the eight main Hawaiian Islands, and also the oldest. 

The volcano that formed Kaua‘i began growing on the seafloor about six million years ago, and by about 4.35 million years ago the volcano’s major shield building phase had finished.

Kaua‘i used to be where the island of Hawai‘i is today, over the Hawaiian magmatic hot spot plume of erupting lava.  Each of the Hawaiian Islands was once over the hot spot lava plume. 

Since the time when Kaua‘i first grew up from the seafloor to become an island it has moved northwest about 320 miles (515 km) on the Pacific Plate.  As Kaua‘i moved away from the active hot spot area, its volcanoes became dormant and then extinct.

Kaua‘i was formed primarily by Olokele Volcano, which once rose to (an estimated) more than 8,500 feet (2,591 m) above sea level.  Millions of years ago the summit of the volcano collapsed.  When the summit of a volcano collapses, it forms what is known as a caldera. 

The collapse of Olokele’s summit formed a caldera 11 miles (18 km) across, now considered the largest caldera in the Hawaiian Islands.  The caldera of the active volcano then gradually filled with layers of pāhoehoe lava. 

These “ponded lavas” are generally level and non-porous, holding rainwater.  This created the high elevation Alaka‘i Swamp, known for its distinctive thick, clay soils and dwarfed vegetation.

Olokele Volcano, the original volcano of Kaua‘i, is now considered extinct and has eroded away.  The height of island has also diminished due to subsidence, a bending downward of the Earth’s crust (and the ocean floor) due to the heavy weight of the island mountains. 

This is a common phenomenon that has occurred on all of the Hawaiian Islands.  In the last 400,000 years, Mauna Loa Volcano has subsided more than 3,400 feet (1,036 m), even as the height grew due to volcanic activity.

The two highest peaks on Kaua‘i are now Mt. Kawaikini at 5,243 feet (1,598 m), and Mt. Wai‘ale‘ale at 5,148 feet (1,569 m).  Mt. Wai‘ale‘ale averages 451 inches (1,146 cm) of rain per year, making it one of the rainiest spots on Earth. 

The rains are produced by the northeasterly tradewinds that are funneled toward Wai‘ale‘ale’s summit by the mountain valleys that stretch from Wailua on the east side of the island to Wainiha on the north shore. 

As the wind rises up these steep valleys the air cools abruptly, forming clouds that rain down upon the land.  Southerly Kona storms also bring moisture up Hanapēpē, Olokele, and other valleys.

At more than five million years old, Kaua‘i definitely qualifies as an ancient Pacific Island.  Centuries of heavy rains on Kaua‘i have caused the extreme erosion that is characteristic of ancient Pacific islands. 

Steep cliffs are common on Kaua‘i, dropping more than 3,000 feet (900 m) straight down in some places along the Nāpali coast, and in the deep rain-carved valleys of spectacular Waimea Canyon.  Layer by layer the process of erosion continues to bring Kaua‘i back to sea level.  Eventually only a coral atoll will remain.

[Photograph: Nāpali coast]

 

Ke alahaka o Nu‘alolo.

The ladder of Nu‘alolo.

The ascent of Nu‘alolo, Kaua‘i, is steep and difficult. In the olden days the people built a ladder in order to go up and down more easily. This ladder is famed in ancient poetry of Kaua‘i.

                                                                        (Pukui: 1672-180)

 

Hawai‘i Island: The Newest and Biggest Hawaiian Island

On the island of Hawai‘i, Mauna Kea Volcano rises some 6.2 miles (10 km) from the seafloor.  The summit of Mauna Kea is 13,796 feet (4,205 m) above sea level, but measured from base to summit the mountain is a phenomenal 33,476 feet (10,200 m) tall. 

While Mauna Kea is the tallest mountain on Earth (measured from base to summit), it is not the largest in our solar system.  That title goes to a volcano on Mars called Olympus Mons, which is 370 miles (595 km) wide and 79,000 feet (24,079 m) high, three times as high as Mt. Everest.

Like all the other Hawaiian Islands, Hawai‘i Island is moving northwest away from the magmatic hot spot area at the rate of about 3½ inches (9 cm) per year.  The Big Island’s volcanoes will eventually become dormant and then extinct. 

In turn, Lō‘ihi will be carried more directly over the erupting hot spot to become the center of volcanic activity and will eventually grow tall enough to rise above the surf and become the next Hawaiian Island.

 

Lava Research Yields Clues to Ancient Earth

The volcanoes of the Hawaiian Islands (shield volcanoes erupting over a stationary magmatic hot spot) erupt a different sort of lava than volcanoes around the edges of the Pacific Plate (stratovolcanoes, produced by tectonic subduction activity).  Researchers now believe that the chemistry of the lava of the Hawaiian Islands’ shield volcanoes may hold clues to the early universe.

Researchers theorize that remnants of the primordial cloud of gas and dust that coalesced to form our solar system some 4.6 billion years ago may have been preserved in the magma (molten earth) near the Earth’s core.  That magma is rising up in the hot spot plume of lava forming the Hawaiian Islands.  This also occurs at numerous other hot spot sites on Earth.

The deep-sourced Hawaiian magmatic hot spot brings the primordial magma from near the Earth’s center to the surface where it is currently erupting from Kīlauea Volcano and Lō‘ihi Seamount. 

The chemical remnants of Earth’s early atmosphere may be detected in this lava.  Ongoing scientific research about Earth’s early environment continues to analyze Hawaiian lavas and the processes of magmatic hot spots.

[Photograph: Hawaiian-Emperor Chain, or suitable photograph]