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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteSea arches collapse because erosion continues after waves carve an opening through a headland. Waves and sediment wear away the arch’s roof and supports until the remaining rock can no longer hold together. Collapse may leave an isolated sea stack, but the timing and immediate trigger depend on local conditions—and are not always known.
How a sea arch forms
- Erosion follows weaknesses in the rock. Waves work on fractures, faults, joints, bedding planes, and softer layers in a headland. Carried sediment can help enlarge these weak zones into sea caves. The National Park Service describes how sea caves form along weaknesses in coastal rock.
- A cave opens through the headland. Continued erosion can cut a cave through to the other side, leaving a natural bridge of rock: a sea arch.
- The arch keeps eroding. The opening exposes the bridge and its supports to ongoing wave action. At Hawaiʻi Volcanoes National Park, the NPS explains that rough surf can strike the back of caves and reflect toward the headland, helping widen openings; erosion does not stop once an arch forms. NPS: Sea Arches
- The bridge eventually fails. As the roof or supports weaken, part or all of the arch may collapse. A detached remnant can remain offshore as a sea stack, while erosion continues to reshape the coast.
How waves wear down an arch
Wave erosion involves more than water simply striking rock. The National Park Service identifies waves as a major erosive force on most coasts, while noting that their effects depend on wave energy and the material being attacked. Breaking waves can trap and compress air against a rock surface; the pressure and impact can dislodge fractured rock and loose particles, a process called quarrying. Waves also move sand, gravel, and other particles against rock, wearing it down through abrasion. NPS: Coastal Processes
Large swell and storms can deliver greater energy, but their presence alone does not establish why a particular arch collapsed. Rock composition and structure, local wave patterns, and climate all influence how a rocky coast changes. A fractured or less resistant section may erode faster than stronger surrounding rock, so the arch’s shape and supports matter as much as the general exposure of the coast. NPS: Rocky Coasts
What happened to Hōlei Sea Arch
Hawaiʻi Volcanoes National Park reported on October 1, 2026, that Hōlei Sea Arch—described by the park as 90 feet (27.4 meters) high—was standing on Wednesday, September 23, and had collapsed by Sunday night, September 27. The exact time is unknown. The collapse may have occurred while the park was temporarily closed during Tropical Storm Nolo, but the National Park Service did not identify the storm as the cause. NPS: Hōlei Sea Arch collapses
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The arch had a documented history of instability. Earthquakes during the 2018 Kīlauea eruption and summit collapse damaged nearby cliffs. New cracks and instability prompted the park to close the original viewing area in January 2020; a safer viewing area opened in March 2020. Later, massive surf during Tropical Storm Darby broke a piece from the arch’s lower section. These events document prior damage and instability, but do not establish one definitive immediate cause for the 2026 collapse. NPS: Hōlei Sea Arch viewing area closed
Why a storm cannot automatically be named as the cause
A collapse observed after a storm is not proof that the storm triggered it. Erosion may weaken an arch gradually, while the final failure happens between observations; the precise moment and mechanism can be difficult to establish. Hōlei’s observation window is known, but the National Park Service did not assign a definitive immediate cause. A useful account separates what was observed—such as prior cracks, rock loss, or the dates when a feature was last seen standing and first found collapsed—from what is suspected and what remains unknown.
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The same caution applies beyond ocean coasts. Glen Canyon National Recreation Area confirmed that Double Arch at Lake Powell, a Navajo sandstone feature, collapsed on August 8, 2024. The park said weathering, wind, and rain had affected it, and that changing water levels and wave erosion were suspected contributors; it also said the cause was not known. Double Arch was at a lake, not an ocean coast, so it is a comparison in careful causal attribution rather than an equivalent coastal example. NPS: Double Arch collapses
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Safety around unstable coastal cliffs
At Hōlei, the National Park Service directs visitors to stay out of closed areas and away from cliff edges, which may collapse without warning. The park also identifies the rough, wave-swept coast as a falling and drowning hazard. Follow closures and keep away from unstable edges; a viewing area designated as safer does not make the surrounding cliffs stable.
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