Eight days at sea just to reach the study area
Beneath the remote expanse of the North Pacific, a T-shaped plateau the size of a small nation has waited in near-total silence since the last human inquiry in 1980. German and Japanese scientists aboard the research vessel SONNE are now returning to Hess Rise — a geological monument born of ancient, convulsive volcanism between 90 and 115 million years ago — to ask how such a structure comes to exist at all. The question is not merely academic: oceanic plateaus are records of the Earth's most transformative interior upheavals, and decoding Hess Rise may rewrite our understanding of how the entire Pacific basin assembled itself.
- One of Earth's largest oceanic plateaus has gone unstudied for over four decades, leaving a 1,000-kilometer gap in our understanding of Pacific geological history.
- Three rival theories — a migrating triple junction, a spreading center origin, or a solitary deep mantle plume — compete to explain how Hess Rise was born, and only hard evidence from the seafloor can settle the debate.
- Reaching the study site alone requires eight days at sea, and the team must deploy up to 40 autonomous seismometers across depths of 2,000 to 5,000 meters in one of the planet's most isolated stretches of ocean.
- A two-phase expedition strategy pairs geophysical mapping now with direct rock sampling later, building a layered case that moves from structural inference toward geological proof.
- If a shared hotspot connects Hess Rise to the neighboring Shatsky Rise, the findings could reveal a recurring pulse of deep-Earth volcanism that shaped the Pacific over tens of millions of years.
Halfway between Japan and Canada, a T-shaped oceanic plateau stretches 1,000 kilometers across the Pacific seafloor. The Hess Rise is among Earth's largest such formations, yet it has received only a handful of scientific visits — the last in 1980. Now, a German-Japanese expedition aboard the research vessel SONNE is returning to ask a question that has lingered for decades: how did this remote geological giant come to be?
Oceanic plateaus like Hess Rise are the scars of extraordinary violence in Earth's interior. During the Middle Cretaceous, between 90 and 115 million years ago, the planet erupted in a prolonged burst of volcanism that produced at least a dozen major plateaus. The mechanics behind these events, however, remain contested. Led by GEOMAR geophysicist Anke Dannowski, the expedition will test three competing models: formation at a migrating triple junction where three tectonic plates once met, growth at a seafloor spreading center, or birth from a deep mantle plume entirely independent of plate boundaries. Researchers will also probe whether the same hotspot responsible for the neighboring Shatsky Rise may have rekindled millions of years later beneath Hess Rise.
The fieldwork is as demanding as the questions. Eight days of sailing are required just to reach the site. Once there, up to 40 ocean bottom seismometers will be dropped to depths between 2,000 and 5,000 meters, recording seismic signals autonomously while ship-based gravity sensors, a towed magnetometer, and multibeam sonar build a picture of the plateau's internal architecture. A follow-up cruise will then collect physical rock samples to ground-truth the geophysical data against geological reality.
Before departing Yokohama, the two national teams gathered aboard the SONNE for a reception marking the start of their collaboration. German schoolchildren from the Tokyo and Yokohama area also came aboard — a small, human moment before the ship turned toward one of the loneliest and most ancient corners of the ocean.
Halfway across the Pacific Ocean, roughly equidistant from Japan and Canada, sits one of Earth's most remote geological puzzles. The Hess Rise is a massive oceanic plateau, shaped like a T and stretching some 1,000 kilometers across the seafloor. Its isolation—thousands of kilometers from the nearest continent—has made it one of the least-visited places on the planet. The last scientific expedition to study it arrived in 1980. Now, after more than four decades, German and Japanese researchers are returning to ask a fundamental question: how did this thing get here?
The answer matters because oceanic plateaus like Hess Rise represent some of the most violent geological events in Earth's history. They form when the planet's interior convulses, sending lava surging upward in waves so massive they cover hundreds of kilometers and pile up tens or hundreds of meters thick. During the Middle Cretaceous period, between 115 and 90 million years ago, the Earth experienced a particularly intense burst of this volcanism. At least a dozen major oceanic plateaus were born during that window. Yet the precise mechanics of how these structures assembled themselves remains unclear. Understanding Hess Rise, researchers believe, will unlock the broader story of how the Pacific basin itself evolved.
The expedition, led by geophysicist Anke Dannowski of GEOMAR Helmholtz Center for Ocean Research in Kiel, will test three competing theories. The first proposes that Hess Rise formed as three tectonic plates converged at a single point—a "Triple Junction"—and that this junction migrated across the seafloor, leaving the plateau in its wake. The second model suggests the plateau grew directly at a spreading center, the zone where new oceanic crust continuously forms as plates pull apart. The third, and perhaps most intriguing, imagines Hess Rise as a solitary creation, born not from plate boundaries but from a mantle plume—a column of superheated rock rising from deep within the Earth's interior. Researchers will also investigate whether the same hotspot that created the neighboring Shatsky Rise 30 million years earlier might have reignited at Hess Rise, producing a second pulse of volcanism millions of years later.
The logistics alone are daunting. Dannowski notes that eight days at sea are needed just to reach the study area from port. Once there, the team will deploy up to 40 ocean bottom seismometers across the seafloor at depths between 2,000 and 5,000 meters. These instruments, dropped from the ship and sinking freely to the bottom, will operate autonomously, recording every tremor and pressure wave. The seismic data will be layered with measurements from ship-based gravity sensors, a towed magnetometer, and multibeam sonar mapping from the research vessel SONNE itself. Together, these tools will reveal the internal structure and composition of the plateau without requiring a single rock sample.
The first expedition, SO320/1, focuses on gathering this geophysical data from the western and northern sections of Hess Rise. A follow-up cruise, SO320/2, will then collect actual rock samples from the seafloor, allowing researchers to determine the age of the material and test the theories against geological reality. Before departure from Yokohama, the German and Japanese teams held a reception aboard the research vessel, a moment of professional exchange before months at sea. German schoolchildren from Tokyo and Yokohama also visited, getting a glimpse of what life looks like when your office is a ship in the middle of the Pacific, and your questions are written in stone at the bottom of the ocean.
Notable Quotes
The Hess Rise is so far from the mainland that we have scheduled eight days at sea just for the transit to the study area.— Dr. Anke Dannowski, expedition leader and geophysicist at GEOMAR
The investigation of Hess Rise will provide insights into the entire geotectonic evolution of the Pacific.— Dr. Anke Dannowski
The Hearth Conversation Another angle on the story
Why does it matter how Hess Rise formed? It's just a bump on the ocean floor.
It's not just a bump—it's a record. These plateaus form during moments when the Earth's interior is in upheaval. Understanding how Hess Rise came to be tells us about the forces that shaped the entire Pacific basin, and about how the planet's deep interior works.
But we already know volcanism created it. What's left to figure out?
We know volcanism was involved, yes. But the mechanism is still unclear. Did it form at a plate boundary, or did it form in isolation from a plume rising from the mantle? Those are fundamentally different stories about how the Earth operates.
And you can tell the difference by dropping instruments on the seafloor?
The seismic data shows us the internal structure—how the rocks are arranged, what they're made of. Combined with rock samples and age dating, we can reconstruct what happened. It's like reading the geological record written in stone.
How long has it been since anyone looked at this place?
1980. Forty-six years. The technology is incomparably better now. We can ask questions we couldn't ask before.
What happens if you find something unexpected?
Then we revise our understanding of how oceanic plateaus form globally. And we might discover that the Shatsky Rise and Hess Rise are connected through the same hotspot, separated by 30 million years but born from the same source.