HONOLULU (KHON2) — Much like post-glacial rebound where the island of Greenland uplifted several inches out of the ocean after a massive glacier fell from its land and into the ocean.
This phenomenon made us wonder if the heaviness of massive construction projects is having an impact on Hawaiʻi’s islands. Are our islands sinking into the ocean?
Just as we began pondering that, the University of Hawaiʻi (UH) at Mānoa made a fascinating discovery.
Parts of Hawai‘i are sinking faster than others, and that’s a big concern for the future.
A recent study by researchers at the UH have discovered that some areas, especially on the island of O‘ahu, are sinking much quicker than scientists originally thought.
This sinking, known as subsidence, could cause major flooding in these low-lying areas much sooner than expected, particularly in urban parts of O‘ahu.
The lead researcher, Kyle Murray, explained that this subsidence is often overlooked when scientists study how sea level rise will affect the islands.
“Our findings highlight that subsidence is a major, yet often overlooked, factor in assessments of future flood exposure,” said Murray, who is the lead author of the study and researcher with the Climate Resilience Collaborative (CRC) at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). “In rapidly subsiding areas, sea level rise impacts will be felt much sooner than previously estimated, which means that we must prepare for flooding on a shorter timeline.”
Since land in some areas is sinking so quickly, these places will experience the effects of rising sea levels much earlier than we thought. In some parts of O‘ahu, land is sinking almost 40 times faster than the average rate, which is only about 0.6 millimeters per year on most of the island.
That’s just a tiny bit every year or about the thickness of 10 sheets of paper. But in certain areas on the south shore of O‘ahu, the land is sinking more than 25 millimeters per year, which is a much faster rate than expected.
“Much of the urban development and infrastructure, including parts of the industrial Mapunapuna area, is built on sediments and artificial fill,” said Murray. “We think the majority of subsidence is related to the compaction of these materials over time.”
So, here are the t op 7 facts about Hawai‘i’s sinking islands problem.
- Parts of Hawai‘i are sinking faster than others: Some areas of the Hawaiian Islands, especially on O‘ahu, are sinking much faster than any could have expected. This sinking is known as “subsidence”.
- Subsidence could lead to faster flooding: Subsidence is causing certain areas to experience flooding from rising sea levels much sooner than anticipated. Some places on O‘ahu are sinking up to 40 times faster than the average rate of 0.6 millimeters per year.
- Urban development plays a role: Many parts of urban O‘ahu, like the Mapunapuna industrial area, are built on artificial fill and sediments. Over time, the weight of these buildings causes the land to sink more quickly.
- Faster sinking than sea level rise: In areas where subsidence is happening quickly, the rate of land sinking is faster than the rate of sea level rise in Hawai‘i. Flood exposure in Mapunapuna could expand by more than 50% by 2050 due to subsidence, while the timeline for flood preparedness may be reduced by up to 50 years. This means impacts will be felt much sooner than previously anticipated.
- The compaction of materials contributes to subsidence: The sinking in certain areas is mostly due to the compaction of materials like artificial fill and sediment used for construction. This causes the land to settle, leading to faster subsidence.
- Flooding will happen sooner than expected: The study revealed that areas experiencing subsidence will face chronic flooding much sooner than previously expected. This means cities and communities need to prepare for flooding on a much shorter timeline.
- Critical data for future planning: The research provides valuable data that can help inform decision-making for flood protection, infrastructure improvements and long-term urban planning in Hawai‘i to ensure the safety of homes, businesses and cultural areas.
This study is a wake-up call, showing how subsidence could change the future of coastal areas in Hawai‘i and why immediate action is needed.
“This rate of land subsidence is faster than the long-term rate of sea level rise in Hawai‘i (1.54 millimeters per year since 1905), which means those areas will experience chronic flooding sooner than anticipated,” said Phil Thompson, study co-author and director of the UH Sea Level Center in SOEST. “In places like the Mapunapuna industrial region, subsidence could increase flood exposure area by over 50% by 2050, while compressing flood preparedness timelines by up to 50 years.”
This research is crucial because it gives important information about the future of coastal areas in Hawai‘i. If subsidence isn’t taken into account, city planners might not fully prepare for the flooding and other challenges coming their way.
“Our research provides critical data that can inform state and county decision-making, helping to improve flood exposure assessments, infrastructure resilience, and long-term urban planning,” said Chip Fletcher, co-author, director of CRC, and interim dean of SOEST. “This work directly serves the people of Hawai‘i by ensuring that local adaptation strategies are based on the best available science, ultimately helping to protect homes, businesses and cultural areas.”
The study provides data to help make decisions on protecting homes, businesses and cultural areas in order to ensure communities in Hawai‘i are ready for whatever comes next.
So, are we sinking Oʻahu? You can click here to read more.