Seeking the climate link to earthquake and volcanic activity

A bold theory suggests that rising global sea levels associated with global deglaciations might lead to an increase in the frequency of earthquakes and volcanic eruptions. And a Marsden-funded team of researchers working off the east coast of Aotearoa New Zealand, at the Hikurangi Subduction Margin, has taken a deep dive into Earth’s past to explore this connection.

Using a remarkable 500-meter-long marine sediment core, extracted by the International Ocean Discovery Programme from beneath 3,520 meters of water, the team has gained access to an exceptionally well-preserved geological archive. This core captures distinct layers formed by ancient earthquakes and volcanic eruptions, offering a rare and detailed record that spans the last 1.8 million years of Earth’s history.

The project was conceived and is led by Associate Professor Lorna Strachan (Waipapa Taumata Rau University of Auckland) and brings together a broad multidisciplinary team of international and national collaborators. It has also supported five postgraduate students, each dedicated to investigating the central research question.

MS student Natasha Ngadi examining marine fossils (left), PhD student Laura McDonald at the IODP Core store in Texas (right) (photos: supplied)

A central focus of the project has been developing an accurate age model for the core. This is a complex task, as methods like radiocarbon dating are only effective for the past 45,000 years. To extend beyond this limit, a range of complementary techniques have been employed. These include the analysis of marine microfossils known as foraminifera, which offer insights into past climate and ocean conditions. The team has also examined fossil pollen and layers of volcanic ash, which provide a vital record of terrestrial change and highlight the strong connections between land and ocean systems.

By weaving together these different strands of evidence, the team has created one of the longest and most detailed records of climate change in New Zealand. This high-resolution timeline spans the past 1.8 million years and reveals 17 glacial-interglacial cycles. The new age model is a powerful tool that helps researchers understand the deep connections between climate, land, and geological activity.

Most of the sediments preserved in the core are thought to have been triggered by large earthquakes. When intense shaking occurs, it can cause submarine landslides that send avalanches of sediment cascading down to the deep seafloor. These deposits act like a long-term seismometer, enabling the reconstruction of past earthquakes over time.

However, untangling this signal has been one of the project's most significant challenges. The seafloor is slowly moving toward New Zealand at a rate of about 6 cm per year, and other forces, like deep ocean currents, storms, and floods on land, can produce similar sediment layers.  On top of that, New Zealand’s coastline has shifted dramatically through glacial and interglacial sea level cycles, adding another layer of complexity.

Ongoing subduction of the Pacific Plate beneath the Australian Plate has had the most profound impact on the sedimentary record. This process has caused colossal slope collapse, driving the carving out of giant submarine canyons along the continental slope, shaping how and where sediments are deposited.

As the project nears completion in 2026, the team is now focused on synthesising the multiple strands of evidence gathered over the years of research. Together, they are working to answer a fundamental question: could climate influence the forces that shape our planet from within?

Additional information: Woodhouse et al. (2022), Trench floor depositional response to glacio-eustatic changes over the last 45 ka, northern Hikurangi subduction margin, New Zealand

Additional information: Strachan et al. (2024), Understanding sedimentary systems and processes of the Hikurangi subduction margin; from Trench to Back-Arc.