Mauna Loa doesn't stop at the shoreline—or even at the seafloor.

The part of Mauna Loa you can see is only the top of the volcano.

USGS describes its flanks continuing about 5,000 m below sea level to the seafloor. Below that, the volcano's enormous weight has pressed the seafloor down by roughly another 8,000 m. Measure from that true base, and Mauna Loa is about 17 km tall.

Mauna Loa's elevation — its summit above sea level — is about 4,170 m.

The 17 km figure is something different: total relief from the volcano's geological base to its summit. It is not an elevation.

The extra depth comes from crustal depression (geologists also call it isostatic loading). A sufficiently massive volcano pushes down the crust beneath it, so its structure extends below the ordinary seafloor. USGS seismologists found the boundary beneath the crust bowed downward by as much as 8 km under Mauna Loa.

That makes 17 km an approximate geological figure, not a surveyed one.

Summit above sea level

≈4,170 mSource value

Flanks below sea level to the seafloor

≈5,000 mSource value

Seafloor depressed beneath the volcano

≈8,000 mSource value

Inferred from seismic studies

Total

4,170 + 5,000 + 8,000 ≈ 17,170 mCalculated

Published

about 17 km from geological baseResult

Approximate — not an elevation

Authoritative approximate geological reference. USGS gives about 17,170 m from true base to summit; the depressed-seafloor portion is inferred from seismic studies, so treat it as approximate.

The ~17 km figure includes geological structure below the seafloor and must not be represented as summit elevation. The geological base-to-summit display value is approximate.

• USGS

  Mauna Loa(opens external site)

• USGS

  Volcano Watch — How high is Mauna Loa?(opens external site)

  Highest point 4,170 m above sea level

• USGS

  Volcano Watch — How high is Mauna Loa?(opens external site)

  Flanks continue another 5,000 m below sea level

• USGS

  Volcano Watch — How high is Mauna Loa?(opens external site)

  Sea floor depressed another 8,000 m

• USGS

  Volcano Watch — How high is Mauna Loa?(opens external site)

  Total relief about 17,170 m

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