Hawaii’s Big Island has gained roughly 1,000 acres of new land from volcanic eruptions in the last decade alone, and thousands more over the past half-century. Nearly all of this growth comes from Kīlauea, one of the most active volcanoes on Earth, which has been erupting almost continuously since 1983. But the story is more complicated than lava simply piling up at the shoreline. New land in Hawaii is constantly being built, collapsed, eroded, and submerged, so the net gain at any given moment depends on which of those forces is winning.
The 2018 Kīlauea Eruption Changed the Map
The single largest land-creation event in recent Hawaiian history came during the dramatic 2018 lower East Rift Zone eruption of Kīlauea. Over roughly three months, massive lava flows poured into the ocean near Kapoho Bay on the Big Island’s eastern coast, filling in the bay entirely and building a broad peninsula of new rock. The eruption added approximately 875 acres of new land to the island, an area larger than New York’s Central Park. Satellite imagery before and after the event shows a coastline that looks nothing like its predecessor, with an entirely new headland jutting into the Pacific.
What made the 2018 eruption so productive as a land builder was the sheer volume of lava. Fissure 8, the dominant vent, fed a river of molten rock that traveled several miles to the coast and entered the ocean continuously for weeks. The lava that reached the sea was unusually fluid and voluminous, which meant it spread out efficiently rather than piling up in unstable heaps. Some of this new land extended more than half a mile beyond the original coastline.
Below the waterline, the story was even bigger. Bathymetric surveys after the eruption revealed substantial submarine lava deltas, essentially underwater extensions of the new land that reached far deeper than what was visible at the surface. These submarine deposits were built from fragmented lava that shattered on contact with cold seawater. Researchers found that the grain size of this fragmented material plays a critical role in how stable the resulting delta is. Coarser fragments, like those produced in 2018, tend to form deltas that experience smaller, more contained landslides, while finer-grained material leads to larger, more dangerous collapses with greater runout distances.1Bulletin of Volcanology. Submarine lava deltas of the 2018 eruption of Kīlauea volcano
Thirty-Five Years of Steady Growth Before 2018
Long before the spectacular 2018 event, Kīlauea had been quietly adding land to the Big Island for decades. The Pu’u ‘Ō’ō eruption, which began in 1983 and continued until 2018, was one of the longest-lived eruptions in recorded Hawaiian history. For most of that period, lava traveled through underground tubes from vents on the volcano’s flank to the southeastern coast, where it entered the ocean and built new shoreline incrementally.
Between 1986 and 1994 alone, about 2 square kilometers (roughly 500 acres) of new land was added to the island from these flows, with an average of 350,000 cubic meters of lava per day feeding through the tube system.2ScienceDirect (Elsevier). Littoral hydrovolcanic explosions: a case study of lava–seawater interaction at Kilauea Volcano During part of that stretch, flows entering the ocean in the Kamoamoa area of Hawaiʻi Volcanoes National Park built a single lava delta 2.9 kilometers long and 500 meters wide.2ScienceDirect (Elsevier). Littoral hydrovolcanic explosions: a case study of lava–seawater interaction at Kilauea Volcano That is a remarkable piece of real estate constructed in just a couple of years.
Over its full 35-year lifespan, the Pu’u ‘Ō’ō eruption is estimated to have added more than 500 acres of new land to the island. Combined with the 2018 eruption, Kīlauea’s output since the early 1980s has pushed the Big Island’s southeastern coastline noticeably outward. If you compare modern maps of the Puna district to those from the 1970s, the difference is visible without any special tools.
Why New Land Does Not Always Stay
Creating land from lava is not a one-way process. A significant fraction of the new shoreline built during eruptions is lost relatively quickly, sometimes within hours or days of being formed. Lava deltas, the flat platforms of new rock that extend outward from the coast, are inherently unstable structures. They sit on foundations of loose, fragmented volcanic debris that accumulated underwater, and they can collapse without warning into the ocean.
These collapses are among the most dangerous hazards at coastal eruption sites. When a section of lava delta suddenly gives way, it can generate explosive steam clouds, hurl rocks hundreds of meters, and produce local tsunamis. The 2018 eruption saw multiple bench collapses along the new coastline, some of them substantial enough to send plumes of debris and steam high into the air. Researchers have described these collapses as one of the most significant but least predictable volcanic hazards at ocean islands.1Bulletin of Volcanology. Submarine lava deltas of the 2018 eruption of Kīlauea volcano
The stability of a lava delta depends heavily on the type of material it is built from. When lava enters the ocean, it shatters into fragments that range from fine sand-sized particles to coarse rubble, depending on the chemistry of the lava, how fast it is flowing, and the conditions at the shoreline. Fine-grained deltas hold water pressure in their pore spaces longer, which means that when they fail, the landslides travel farther and are more destructive. Coarser deltas drain more quickly, so their collapses tend to be smaller and more localized.1Bulletin of Volcanology. Submarine lava deltas of the 2018 eruption of Kīlauea volcano This means the 875 acres added in 2018, built mostly from relatively coarse material, may prove more durable than some of the land added during the Pu’u ‘Ō’ō era.
Subsidence Slowly Swallows the Islands
Even land that survives the initial collapses faces a slower, quieter threat. The entire Hawaiian island chain is gradually sinking under its own weight. As volcanic eruptions pile more and more rock onto the oceanic crust, the lithosphere beneath bends downward, a process geologists call flexure. This means that while the Big Island’s active volcanoes are building it up, the sheer mass of the rock is simultaneously pushing the island down into the mantle.
This sinking is not just theoretical. Continuous GPS stations across the Hawaiian Islands record ongoing vertical displacement, and satellite-based radar measurements confirm that coastal areas are subsiding at rates that matter for long-term planning.3Communications Earth & Environment. Coastal land subsidence accelerates timelines for future flood exposure in Hawai’i The subsidence is especially pronounced on the Big Island, where the volcanic load is greatest and most recently deposited. But the older islands feel it too. Surveys around Oahu and the islands of the Maui Nui Complex have identified 89 separate submerged terraces on the volcanic flanks of those islands, representing former shorelines and reef platforms that were once at or near sea level and have since sunk beneath the waves.4Geochemistry, Geophysics, Geosystems. Unraveling the tilting history of the submerged reefs surrounding Oahu and the Maui‐Nui Complex, Hawaii
Those terraces tell a striking story. The islands of Maui, Molokai, Lanai, and Kahoolawe were once connected as a single large island, sometimes called Maui Nui, before subsidence and erosion broke them apart and drowned the lowlands between them. The shallow channels separating those islands today are remnants of what was once dry land. In a sense, Hawaii has lost far more land to subsidence over geological time than it has gained from recent eruptions, though the timescales are so different that the comparison is a bit misleading.
Erosion at the Shoreline
Subsidence is not the only force shrinking Hawaii’s coastline. Wave erosion, storm surges, and rising sea levels are steadily eating away at beaches across the island chain, even on shores that have nothing to do with recent volcanic activity. A study examining decades of shoreline change across the state found that Maui has been hit hardest, with about 78% of its beaches eroding over the past century. Oahu fared somewhat better but still saw 52% of its beaches retreat. The average rate of shoreline loss on Maui was roughly 0.13 meters per year, compared to about 0.03 meters per year on Oahu.5ScienceDirect (Global and Planetary Change). Are beach erosion rates and sea-level rise related in Hawaii?
These numbers are interesting because they show that the rate of beach erosion far outpaces the rate of sea-level rise itself, by about two orders of magnitude.5ScienceDirect (Global and Planetary Change). Are beach erosion rates and sea-level rise related in Hawaii? Sea-level rise is a contributing factor, but the actual retreat of Hawaii’s shoreline is driven more powerfully by wave energy, sediment loss, and human development along the coast. This matters for the big-picture question of how much land Hawaii is gaining or losing. On the Big Island’s active southeastern flank, volcanic eruptions are adding acreage. But on most other shorelines across the state, the islands are getting smaller, not bigger.
The net result depends entirely on where you are looking. If you focus only on the Puna coast, Hawaii has grown substantially in recent decades. If you zoom out to the full archipelago, the picture is more mixed. The older islands like Oahu, Maui, and Kauai, which no longer have active volcanism to replenish their coastlines, are in a long, slow process of shrinking.
How Life Colonizes Fresh Lava
New volcanic land starts as a lifeless expanse of black rock, but it does not stay that way for long. The process of ecological succession on Hawaiian lava flows has been well studied, and the pace at which life takes hold depends primarily on two factors: how much rain the area receives and how old the flow is. Warmer, wetter sites see vegetation establish faster, while dry, exposed flows can remain barren for decades or even centuries.
Research on ecosystem development across Hawaiian lava flows of different ages found that plant biomass and species richness were strongly tied to precipitation and flow age, but not much affected by temperature or lava texture on its own.6Journal of Vegetation Science. Ecosystem development on Hawaiian lava flows: biomass and species composition That said, the type of lava surface does play a more subtle role. On wet sites, the rough, broken surface of ʻaʻā lava tends to collect soil and moisture in its crevices, giving plants a foothold more quickly. On dry sites, the smoother surface of pāhoehoe lava is actually more hospitable because it retains what little moisture falls rather than letting it drain away.6Journal of Vegetation Science. Ecosystem development on Hawaiian lava flows: biomass and species composition
The first colonizers are typically lichens, algae, and ferns, particularly the native ʻamaʻu fern, which can establish in cracks within just a few years of an eruption. Over decades, a thin soil layer develops from a combination of decomposing organic material, windblown dust, and the gradual chemical breakdown of the basalt itself. Eventually, native ōhiʻa lehua trees take root, and within a century or two, a young native forest can cover what was once a barren lava field. The 500 acres built during the Pu’u ‘Ō’ō eruption are currently in the early stages of this process, with pioneer species already appearing on the older portions of the flow.
Mapping Growth With Lasers
One reason we can now quantify land creation so precisely is the development of lidar, a technology that uses laser pulses to create extraordinarily detailed three-dimensional maps of the ground surface. Airborne lidar surveys can accurately map lava flow boundaries even in areas covered by dense vegetation, because the laser pulses penetrate through gaps in the canopy and bounce off the bare earth beneath.7Geosphere. How lava flows: New insights from applications of lidar technologies to lava flow studies
This capability has been a game-changer for volcanology in Hawaii. Before lidar, mapping a lava flow’s thickness, extent, and volume required painstaking ground surveys that could take months and carried real danger in active eruption zones. Now, researchers can fly over an area before and after an eruption, generate high-resolution elevation models of both surfaces, and subtract one from the other to produce a detailed map of exactly where lava was deposited and how thick it is at every point.7Geosphere. How lava flows: New insights from applications of lidar technologies to lava flow studies The same technique works underwater with sonar-based bathymetry, which is how scientists documented the massive submarine lava deltas from the 2018 eruption.
These measurements have also revealed features that were invisible before: subtle surface folds and cracks that indicate how lava was moving as it cooled, hidden flow channels beneath vegetation, and fine-scale variations in thickness that tell scientists about the dynamics of emplacement. For the question of how much land Hawaii has gained, lidar means we no longer have to estimate. We can measure it down to centimeters.
Lōʻihi and the Next Hawaiian Island
The newest member of the Hawaiian family is not even visible yet. Lōʻihi Seamount sits about 35 kilometers off the southeast coast of the Big Island, rising from the ocean floor to within roughly 975 meters of the surface. It is an active submarine volcano sitting directly over the same hotspot that built every island in the chain, and it is slowly growing upward with each eruption.
At current estimated growth rates, Lōʻihi is not expected to break the ocean surface for tens of thousands of years, possibly much longer. Volcanic island building is not a steady conveyor belt; it involves long pauses, spurts of intense activity, and episodes of collapse. Lōʻihi has already experienced at least one major summit collapse, which set back its progress significantly. But barring some fundamental change in the hotspot’s activity, it will eventually emerge as a new island and, given enough time, likely merge with the Big Island as eruptions from both volcanoes fill in the gap between them.
This is how the Big Island itself was assembled. It is not a single volcano but a composite of five distinct shield volcanoes whose flows overlapped and merged over hundreds of thousands of years: Kohala, Mauna Kea, Hualālai, Mauna Loa, and Kīlauea. Mauna Loa and Kīlauea are still active, and their ongoing eruptions continue to reshape the island. The process that turned five separate volcanic cones into a single island is the same process that will eventually incorporate Lōʻihi into the whole. Meanwhile, far to the northwest, the older Hawaiian Islands continue their slow descent beneath the waves, destined to become the atolls and then the submerged seamounts that make up the Emperor chain stretching thousands of miles toward the Aleutians. Hawaii is simultaneously growing at one end and disappearing at the other, a geological conveyor belt that has been running for more than 80 million years.