Hawaii is sinking faster than expected

In what can only be defined as a peculiar twist of nature, parts of Hawaii are descending faster than others. The implications of this recent discovery are far-reaching, with potential consequences for residents, businesses, and infrastructure.

The study was led by researchers at the University of Hawai’i at Mānoa. The results show that the most vulnerable areas are the low-lying regions that were thought to be at risk much later, particularly urban areas in Oahu.

“In Hawai’i, impacts of sea level rise (SLR) are already widely observed, and include beach loss, coastal erosion, and flooding in the form of direct marine inundation, storm-drain back-flow, as well as groundwater inundation,” noted the researchers.

Understanding sea level rise (SLR) – the basics

As the planet warms, glaciers and ice sheets melt, dumping more water into the oceans. At the same time, seawater expands as it heats up, pushing shorelines further inland.

Coastal cities, small islands, and low-lying areas are already feeling the effects, with flooding becoming more frequent and storm surges hitting harder.

Places like Miami, Jakarta, and the Maldives are on the front lines, watching the ocean creep closer every year.

Rising seas threaten entire communities, displacing millions and damaging infrastructure. Saltwater seeps into farmland, ruining crops, and stronger storms tear through coastal defenses.

Some cities are building seawalls and flood barriers, while others are planning for managed retreat, basically relocating people before disaster strikes.

Sinking land and rising seas

The investigation focused on the impact of sinking land masses amid the ongoing rise of sea levels – a striking contrast that could set the stage for severe flooding issues in Hawaii.

Kyle Murray, the lead author of the study, emphasized the gravity of the situation.

“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,” said Murray.

Predicting the flooding impacts

The UH Mānoa team dedicated nearly two decades to examining satellite radar data to assess the vertical land movements across the Hawaiian Islands with unprecedented precision.

The researchers meticulously plotted the coastal topography using a high-resolution digital elevation model. They incorporated advanced geospatial analysis to track even the most subtle shifts in elevation.

The objective was simple but challenging: to create a comprehensive and dynamic model showing how the juxtaposition of sinking land masses and rising sea levels would amplify future floods, particularly in vulnerable urban and coastal areas.

The sinking speed of Hawaii’s islands

Islands in the Hawaiian chain slowly sink as they move farther from the hotspot beneath the Big Island. This geological process has shaped the archipelago for millions of years.

Given their immense weight and the shifting tectonic plates beneath them, this movement is expected. What comes as a surprise, however, is the rate of their descent, which varies significantly across different regions.

On Oahu, for instance, the subsidence rate each year is quite minimal – about 0.6 millimeters, which is roughly the thickness of 10 sheets of standard printing paper. This is a seemingly negligible shift on a year-to-year basis.

However, localized spots on Oahu’s south shore present a different narrative, with land sinking at a staggering 40 times faster speed, clocking over 25 millimeters per year – a rate that drastically alters flood risk projections and coastal resilience planning.

This study reveals that parts of the Mapunapuna industrial region and similar areas are built on unstable sediments and artificial fill, which are compacting at an accelerated rate. This process is driving increased and uneven subsidence.

Chronic flooding will arrive early

According to Phil Thompson, a co-author of the study, this rapid subsidence rate outstrips the sea-level rise rate in Hawaii – which has maintained an average of 1.54 millimeters annually since 1905.

Therefore, chronic flooding is bound to happen sooner than initially expected. In regions like Mapunapuna, this could translate to more than a 50% increase in flood exposure area by 2050 while cutting flood preparedness timelines in half. This presents a serious challenge for Hawaii.

Urgency of Hawaii’s sinking regions

When the findings of this study are considered, it is evident that the shoreline plays a major role in maintaining the viability of Hawaii’s coastal communities, economy, and infrastructure.

It is thus imperative for urban planning and coastal adaptation strategies to take these findings into account so that the urgency of mitigation efforts is not underestimated.

“This work directly serves the people of Hawaii by ensuring that local adaptation strategies are based on the best available science, ultimately helping to protect homes, businesses, and cultural areas,” said study co-author Chip Fletcher, director of CRC and interim dean of SOEST.

Ultimately, Hawaii’s sinking regions serve as a quiet reminder that nature follows its own timeline. As we look ahead, a deep understanding of these forces is crucial for strengthening our communities and infrastructure against future challenges.

The full study was published in the journal Communications Earth & Environment.

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