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Hawaii is known across the world for its iconic volcanoes that dot the islands and have helped shape their landscapes over millions of years. But why does Hawaii have so many volcanoes when most places do not?

If you’re short on time, here’s a quick answer to your question: Hawaii’s location over a hot spot in Earth’s mantle provides the heat needed to produce volcanic eruptions that have built up the islands over time.

In this comprehensive guide, we’ll explore the geologic processes that cause Hawaii’s volcanic activity, how the islands formed from underwater eruptions, the different types of volcanoes found in Hawaii, and how scientists monitor for signs of future eruptions.

Hawaii’s Tectonic Plate Location Allows Hot Spot Volcanic Activity

Hawaii lies above a mantle plume hot spot

The Hawaiian islands sit above a fixed mantle plume hot spot deep beneath the Earth’s crust. This hot spot is an area where hot mantle material rises up from near the Earth’s core, creating a plume-like structure in the mantle.

The hot spot supplies magma from the Earth’s interior to the base of the Pacific tectonic plate. As the Pacific plate slowly drifts northwestward over this Hawaiian hot spot at a rate of approximately 7 centimeters per year, the magma from the hot spot continuously breaks through the plate to create Hawaii’s active volcanoes.

This hot spot is estimated to have existed for at least 80 million years. As the Pacific plate drifts across it, a chain of volcanoes is created with the newest island closer to the hot spot and older islands further away.

Hawaii’s Big Island hosts the currently active volcanoes of Mauna Loa and Kilauea, sitting directly above the hot spot.

The movement of the Pacific Plate allows continuous volcanic activity

The Pacific tectonic plate’s northwesterly movement over the fixed Hawaiian mantle plume hot spot not only forms the island chain but allows for the nonstop volcanic eruptions that characterize Hawaii.

Since the hot spot continually provides molten rock to the base of the plate, volcanic activity gets prolonged as the magma always has access to the surface.

The Pacific plate area containing the Hawaiian hot spot is also known as the Hawaiian swell. As volcanoes from past movement pile up on the ocean floor, their massive weight presses down on and warps the plate below, creating this raised swell in the plate to support them.

This swell gives magma from the hot spot extra boost to make it through the crust, feeding Hawaii’s active volcanoes.

Together, the combination of Hawaii’s location on a drifting tectonic plate above a mantle plume hot spot creates the ideal conditions for ongoing volcanic activity that formed the islands and continues building them today. U.S.

Geological Survey (USGS) Hawaiian Volcano Observatory provides updated monitoring and research on Hawaii’s eruptions.

How Hawaii’s Islands Formed from Underwater Volcanic Mountains

The Hawaiian Islands were formed by underwater volcanoes. As the Pacific tectonic plate moved slowly northwestward over a hot spot deep underneath the ocean, volcanoes erupted through the crust, building up islands from the seafloor over millions of years.

The Hot Spot Theory

The prevailing scientific theory about the formation of the Hawaiian Islands is called the “hot spot theory.” According to this theory, the Pacific tectonic plate has been moving over a fixed hot spot deep underneath that has been erupting magma up through the crust for at least 80 million years.

As the tectonic plate drifts across this hot spot at a rate of about 3.9 inches per year, chains of volcanoes have formed. The hot spot continues to remain stationary deep beneath the Pacific Ocean.

Constant Eruptions Building Islands

Over hundreds of thousands and even millions of years, the constant eruptions from the hot spot built up underwater mountains called seamounts. Eventually, some of the tallest seamounts emerged from the ocean as islands we now call Hawaii.

The southeastern most main island called Hawaiʻi Island is still located over the hot spot. The volcanic eruptions occurring there are adding new land to the island each year.

Age and Evolution of the Islands

There is a clear age progression amongst the islands. The southeast islands are still volcanically active and the most unweathered. In contrast, the northwest islands are older and more eroded by wind and waves over millions of years in the ocean.

  • Hawaiʻi Island: less than 0.7 million years old
  • Maui Island: about 1.3 million years old
  • Oʻahu Island: 3.4 million years old
  • Kauaʻi Island: about 5 million years old

Eventually, the northwest islands will sink back below sea level after they have drifted away from the hot spot.

This ongoing cycle of volcanic eruptions, island building, erosion, and subsidence into the sea has created the over 1,500 mile long chain of islands, atolls, banks, seamounts, and shoals comprising the Hawaiian–Emperor seamount chain over 80 million years.

Types of Volcanoes Found in the Hawaii Island Chain

Shield Volcanoes

The majority of volcanoes in Hawaii are shield volcanoes, which are formed by highly fluid basaltic lava flowing in streams across the land over a hot spot deep in the Earth’s mantle. Hawaii’s shield volcanoes have very gentle slopes, creating a rounded shield-like shape as layer upon layer of lava accumulates.

Famous shield volcanoes in Hawaii include Mauna Loa and Kilauea on the Big Island, which erupt frequently and are still active today.

Cinder Cone Volcanoes

In contrast to shield volcanoes, Hawaii also has a number of cinder cone volcanoes formed from more viscous basaltic lava. As the thick lava is blown into the air during an eruption, it breaks into cinder-like fragments that fall around the vent, building up a steep conical hill.

Cinder cones are smaller and steeper than shield volcanoes. For example, Pu’u ‘O’o cinder cone located on Kilauea erupted nearly continuously from 1983 to 2018, adding around 500 feet to its height.

Caldera Volcanoes

Some of the volcanoes in Hawaii formed calderas, which are large crater-like depressions created when a volcano partially collapses following an eruption and evacuation of its underground magma chamber.

The summit caldera of Kilauea, called Halema’uma’u Crater, is around 3,500 feet wide and 500 feet deep. Geologists believe calderas ultimately become extinct and erosion will eventually wear down the remaining volcanic mountain.

Clearly, the volcanic hot spot underlying Hawaii has given rise to shield volcanoes, cinder cones, and calderas throughout the island chain. Understanding these volcanic landforms and their origins helps scientists predict future activity and volcanic hazards for Hawaii residents and visitors.

Monitoring Hawaii’s Active Volcanoes for Future Eruptions

Tracking earthquakes and ground swelling

Scientists closely monitor seismic activity and ground deformation to predict future volcanic eruptions in Hawaii. They use sensitive seismographs to detect thousands of small earthquakes at Kīlauea and Mauna Loa each year.

Swarms of small quakes often precede eruptions by hours or days as magma moves through subterranean tubes toward the surface. GPS instruments and tiltmeters also measure bulging flanks and uplift on volcano slopes, which can signal rising magma.

Measuring gas emissions

Monitoring volcanic gas emissions provides another clue to forecast coming eruptions. Scientists regularly measure sulfur dioxide and other gases emerging from fumaroles (steam vents) and other openings.

Increased venting often happens when fresh magma rises into the shallow reservoir below the summit. For example, sulfur dioxide tripled right before Kīlauea’s 2018 eruption. Analyzing the chemical composition of the released gases also reveals what is happening deeper below the surface.

Analyzing lava samples

Geologists conduct lava analysis to uncover evidence about the current state of Hawaii’s active volcanoes. By studying the minerals and chemistry of solidified lava from previous flows, they can estimate the temperature, depth, and composition of the subsurface magma chambers.

This helps determine how much molten rock is available and if hotspot plumes are rising up from the mantle. For instance, lava chemistry suggested that Kīlauea’s magma reservoir was almost empty after months of vigorous eruption in 2018.

Careful monitoring provides the best glimpse into the inner workings of Hawaii’s volcanoes. Tracking seismicity, ground movement, gas emissions, and lava composition enables scientists to constantly assess eruptive potential.

While predicting exactly when lava and ash will burst forth is impossible, regular surveillance offers alerts for aviation and public safety. It also expands scientific knowledge of volcanic processes, improving future forecasting accuracy.

Conclusion

Hawaii’s iconic volcanoes are ultimately caused by its location over a persistent hot spot in Earth’s mantle that allows magma to constantly breach the surface. Understanding the geological processes that built the Hawaiian islands chain over millions of years helps scientists anticipate volcanic hazards to protect local populations.

The volcanic peaks that form the Hawaii islands will continue building up over hundreds of thousands of years until the Pacific Plate shift moves them away from the hot spot’s underground magma source, leaving behind dormant volcanoes while new islands take shape.

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