What this episode covers

• Why Mauna Loa is the largest volcano on Earth

• How plate tectonics and mantle hotspots create volcanic island chains

• The basics of lithosphere, isostasy, and why Earth’s plates move

• How gravity measurements reveal what lies beneath volcanoes

• Why the Ninole Hills are geologically unusual

• Competing hypotheses for their origin—and why most fail

• Evidence for ancient rift zone migration at Mauna Loa

• What this tells us about volcanic evolution and instability

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Why this episode matters

Mauna Loa’s surface is constantly being repaved by lava, hiding its deeper history. The Ninole Hills stand out as an exception—exposing rocks more than 100,000 years old on a volcano where 90% of the surface is younger than 4,000 years.

Understanding how and why these hills survived reveals:

• How volcanic rift zones can move or reorganize

• How massive volcanoes interact with their own weight

• Why geophysics is essential when geology alone cannot see underground

This episode demonstrates how slow, careful science uncovers stories hidden beneath Earth’s surface.

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The scientific setting

The Hawaiian Islands formed as the Pacific Plate moved over a relatively fixed mantle hotspot. As the plate drifted northwest, new volcanoes formed while older ones became extinct, leaving a clear geological trail stretching thousands of kilometers.

Mauna Loa sits near the center of this system—overlapping with neighboring volcanoes like Kīlauea and Mauna Kea—making its internal structure and history particularly complex.

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Key concepts explained

Plate tectonics and isostasy

Earth’s lithosphere behaves like a rigid shell floating atop hotter, deformable material. Add mass—like a giant volcano—and the crust bends and flexes. This process, known as isostasy, plays a key role in volcanic stability and deformation.

Hotspots and rift zones

Hotspots generate magma deep in the mantle. As magma rises and intrudes into the crust, it creates rift zones—linear regions of weakness where eruptions preferentially occur. These zones are dynamic, unstable, and capable of migrating over time.

Gravity as a geophysical tool

By measuring tiny variations in Earth’s gravitational field, scientists can detect differences in subsurface density. Dense materials—such as cooled magma bodies rich in olivine—produce measurable gravity anomalies, allowing researchers to “see” underground structures without drilling.

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Research focus: the Ninole Hills

The Ninole Hills are a small set of topographic highs on the southeastern flank of Mauna Loa. They:

• Expose the oldest known surface rocks on the volcano

• Sit apart from Mauna Loa’s current rift zones

• Display a strong positive gravity anomaly beneath them

These features rule out explanations such as landslides, faulting alone, or remnants of a separate volcano.

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Key questions explored

• Are the Ninole Hills remnants of an ancient summit?

• Could they be the result of faulting or massive landslides?

• Do they mark the location of a former rift zone?

• If so, why did that rift zone move—and how quickly?

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What the evidence shows

Gravity data reveal an elongated high-density structure beneath the Ninole Hills, parallel to—but distinct from—Mauna Loa’s current southwest rift zone. When combined with geochemistry, seismic studies, and island-wide gravity surveys, the only model that fits all observations is rift zone reorganization.

Roughly 200,000 years ago, Mauna Loa’s southwest rift zone likely passed through the Ninole Hills before relocating to its present position. This shift appears to have occurred rapidly in geological terms, driven by changes in volcanic stress and crustal flexure caused by the immense mass of the island itself.

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Episode context

This episode offers a rare, behind-the-scenes look at how geophysical research is conducted—from hiking volcanic slopes with a gravimeter to correcting data for elevation, topography, and deep crustal signals. It also reflects on the long arc of scientific work: how papers age, how interpretations sharpen, and how volcanoes quietly reshape themselves over time.

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Frequently asked questions

What are the Ninole Hills?
A set of small hills on Mauna Loa’s southeast flank exposing unusually old volcanic rocks.

Why are they important?
They preserve evidence of Mauna Loa’s early structure and reveal past rift zone movement.

How do scientists study buried volcanic features?
Using geophysics—especially gravity, seismic imaging, and geochemistry.

Is Mauna Loa still changing today?
Yes. Like all large volcanoes, it remains dynamic, with rift zones, magma systems, and stresses evolving over time.

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Episode details

• Podcast: Whimsical Wavelengths

• Season: 1

• Episode: 12

• Host: Dr. Jeffrey Zurek

• Topic areas: Volcanology, geophysics, plate tectonics, gravity methods, Hawaiian volcanoes

• Based on: Peer-reviewed research published in Geophysical Research Letters (2015)

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Join the conversation

If you enjoyed this deep dive into volcanic evolution, explore the back catalogue of Whimsical Wavelengths—especially episodes featuring guest scientists. Share the episode, leave a review, and reach out with questions or topic suggestions. Science is better when it’s shared—and occasionally punctuated by terrible dad jokes.