Hawaii is one of the few places on Earth where new territory is regularly added to the coastline, driven by constant volcanic activity. This expansion is a dynamic and destructive geological process fueled by the persistent eruption of Kīlauea, one of the world’s most active volcanoes. New land creation occurs in dramatic pulses where molten rock flows directly into the Pacific Ocean. This phenomenon increases the surface area of the Big Island.
The Mechanism of Coastal Expansion
New land forms when superheated lava flows descend the volcano slopes and encounter the cooling power of the ocean water. As the approximately 2,000°F molten rock enters the sea, it rapidly shatters and fragments, creating a foundation of unconsolidated rubble on the seafloor. This debris, known as hyaloclastite, builds up a submerged platform that extends the coastline outward.
The solid lava flow then continues to pour over this unstable underwater slope, forming a feature known as a lava delta. The interaction between the lava and seawater also generates violent steam explosions and a hazardous plume called “laze,” or lava haze. This plume is a mixture of hydrochloric acid steam, fine glass shards, and volcanic gases that poses a serious respiratory and eye irritant hazard.
Key Eruptions Contributing to New Land
The vast majority of new land created in recent decades stems from the Kīlauea volcano on the Island of Hawaiʻi. The Puʻu ʻŌʻō eruption, which lasted nearly continuously from 1983 to 2018, was responsible for the island’s steady growth over a long period. During its 35-year run, this continuous flow of lava consistently built and rebuilt the coastline along the volcano’s southeastern flank.
The largest and most rapid land addition of the modern era occurred during the 2018 lower East Rift Zone eruption. Though it lasted only a few months, this explosive event dramatically altered the Puna coastline. High-volume flows of lava poured into the ocean, completely filling and obliterating Kapoho Bay and the adjacent Vacationland subdivision. This single event created a significant new headland, permanently reshaping the easternmost point of the island.
Quantifying the Total Area Added
The long-term Puʻu ʻŌʻō eruption, which lasted from 1983 until 2018, added approximately 439 acres (177 hectares) to the Big Island’s shoreline. This figure represents the net gain from years of lava entering the sea, offset by coastal erosion and delta collapses. The 2018 lower East Rift Zone event delivered a substantial and rapid expansion, adding an estimated 875 acres of new land in a matter of weeks. The total new area created by these two major, overlapping eruptions over the past few decades is around 1,314 acres (5.32 square kilometers).
Accurate quantification of the new land is challenging because the lava deltas are constantly being built and destroyed. Geologists must continuously map the coastline using aerial surveys and satellite imagery to track the net change. The 875 acres added in 2018 represents one of the largest single additions of land in Kīlauea’s recorded history.
Stability and Features of Newly Formed Coastline
The new land created by lava flows is highly unstable and remains a significant hazard for years after the eruption stops. These lava deltas are structurally weak, consisting of a solid surface crust sitting on a steep, underwater slope of fragmented volcanic material. This foundation makes them susceptible to sudden, massive collapses into the ocean.
Large cracks parallel to the shoreline often appear on the surface of the new land, signaling an imminent collapse. When a portion of the delta gives way, it can trigger explosive activity, hurling large, hot rocks and debris both inland and out to sea. The new coastline is a sterile, black landscape of rough pāhoehoe and ‘a’ā lava, which is slow to support vegetation. Legally, any land created beyond the original shoreline is considered an “extension” and immediately vests in the State of Hawaiʻi, held in public trust.