Off South Maui, Molokini draws a slender curve across the ocean. Beyond it, Kahoʻolawe occupies a longer stretch of the horizon. From shore, their outlines reveal little of their scale—or of the forces that shaped them.

One is the exposed rim of a volcanic cone whose foundation lies underwater. The other is an island where restoring vegetation begins with repairing the ground beneath it. Between them and Maui, the channels conceal the remnants of a much larger landscape.

To understand this view, start below the surface.

Where fire met water

Molokini’s crescent began with an eruption through shallow seawater. As molten rock encountered water, steam expanded rapidly, helping tear the lava into fragments. Those fragments accumulated into a volcanic cone along Haleakalā’s southwest rift zone.

The U.S. Geological Survey estimates that Molokini erupted approximately 230,000 years ago, with a significant uncertainty of about 90,000 years in either direction. The cone rises roughly 500 feet from Haleakalā’s underwater flank, although its summit reaches only about 162 feet above sea level.

Even its color carries evidence of its formation. Water cooled the lava fragments rapidly, creating volcanic glass. As that glass altered into clay minerals, it produced Molokini’s earthy yellow tones—a visible trace of the encounter between molten rock and ocean.

The northern crater rim lies beneath the water. The surviving southern rim forms the curve visible today, the uppermost portion of a volcanic structure largely hidden by the sea.

Two worlds, one crater

Molokini supports two distinct worlds. The exposed land above the water is a protected state seabird sanctuary, closed to ordinary public access. The surrounding waters welcome snorkeling and scuba diving under marine conservation rules.

Above the waterline, ʻuaʻu kani, or wedge-tailed shearwaters, nest in burrows, while ʻiwa, or frigatebirds, soar overhead. Restricting access to the land helps protect nesting sites from disturbance and trampling. The curved rim that frames a snorkeling excursion is also a refuge where seabirds can raise their young.

Below it, the crater opens into a landscape of coral, basalt boulders, and patches of sand. Snorkelers look down into the shallower inner cove, while scuba divers explore its contours beneath the surface. Along the northwestern edge, a reef lies in less than 30 feet of water. Elsewhere, the crater floor slopes toward approximately 100 feet before dropping away.

The outer southern face offers a different experience. Here, Molokini’s back wall falls steeply into water more than 200 feet deep. Experienced divers explore along this submerged face, where scattered coral, crevices, and outcroppings provide habitat for fish. The wall’s scale reveals how much of the volcanic cone remains hidden beneath the ocean. Strong currents and abrupt changes in depth make conditions, training, and knowledgeable guidance essential to planning a dive.

Established in 1977, the approximately 77-acre Molokini Shoal Marine Life Conservation District protects this underwater environment. Observing without feeding fish, disturbing marine life, or removing coral helps preserve the habitat that makes these encounters possible.

Seen through a dive mask, Molokini’s volcanic history takes shape in the reef’s contours and the sheer descent of its outer wall.

The ground beneath recovery

Across the channel, Kahoʻolawe’s story unfolds through soil, wind, and scarce water. The island sits in Haleakalā’s rain shadow, where dry conditions make vegetation especially important—and its loss especially consequential.

Long before ranching and military use, Kahoʻolawe supported coastal fishing settlements, agriculture, and an adze quarry. It also served as a center for navigation. Nearly 3,000 archaeological and historical sites and features have been inventoried, recording a landscape shaped by generations of activity.

During decades of ranching, uncontrolled grazing stripped vegetation and accelerated soil erosion. Decades of military bombing scarred the terrain and left unexploded ordnance, complicating access and restoration long after the bombing ended. Beginning in 1976, Protect Kahoʻolawe ʻOhana organized occupations and legal challenges to end the bombing. Those efforts helped lead to President George H. W. Bush ordering a halt in 1990.

Senator Daniel K. Inouye subsequently sponsored legislation authorizing the island’s return and funding unexploded ordnance removal. The U.S. Navy transferred ownership of Kahoʻolawe to the State of Hawaiʻi in 1994; control of access followed in 2003. The Kahoʻolawe Island Reserve Commission’s historical timeline traces these milestones and the island’s transition toward restoration.

Recovery requires more than planting. In severely eroded areas, exposed ground has become hardpan: compacted soil that cannot readily absorb water. A seedling needs moisture, but the damaged surface resists the very rainfall that could sustain it.

The commission’s work combines native planting with erosion control and invasive-species management. As of 2026, it reports that more than 450,000 native plants have been reintroduced. Trees, shrubs, vines, grasses, and herbs are part of an effort to rebuild living cover across the island.

Research has followed that effort into the watersheds. USGS scientists monitored streamflow, sediment transport, and erosion in Kaulana and Hakioawa to help assess restoration’s effectiveness. The connection runs from upland soil to coastal water: what happens on the slopes can travel downhill.

From Maui’s shoreline, the restoration work is too distant to see. On Kahoʻolawe itself, each planting is part of a larger effort to restore vegetation and reduce soil loss.

An island beneath islands

Farther back in time, these channels were part of a different geography.

Approximately 1.2 million years ago, Maui Nui encompassed about 5,640 square miles—roughly 50 percent larger than today’s Hawaiʻi Island. Maui, Molokaʻi, Lānaʻi, and Kahoʻolawe belonged to this extensive landmass, along with areas now submerged.

Its boundaries changed as the volcanic foundations subsided and global sea levels rose and fell. Growing glaciers lowered sea levels, exposing land; melting ice raised them, allowing water to cover the low connections between volcanoes.

Separation happened gradually. Kahoʻolawe’s connection to Maui disappeared permanently approximately 200,000 to 150,000 years ago. Maui, Lānaʻi, and Molokaʻi remained connected intermittently, most recently around 18,000 years ago.

Those former connections helped plants and animals spread across the landscape, contributing to the biological similarities among islands now divided by ocean. USGS’s account of Maui Nui explains how subsidence and changing sea levels reshaped this larger island.

Along South Maui’s shore, the horizon offers a glimpse of this continuing story. Molokini preserves evidence of an eruption. Kahoʻolawe holds the work of recovery. The channels trace the disappearance of land that once joined neighboring islands.

Look again, and the spaces between the islands become as interesting as the islands themselves.