Well, it just so happens that there is a geological cousin of Dorothy’s fabled path to Oz, but this one exists more than 3,000 meters beneath the Pacific, north of the Hawaiian Islands. In 2022, exploration vessel E/V Nautilus caught this surrealist scene within the expansive Papahānaumokuākea Marine National Monument on the Liliʻuokalani Ridge: a dry-looking lakebed fractured into neat, 90-degree angles in what looked for all the world like a perfect “yellow brick road.”
It is not man-made but the product of intense submarine volcanism. Researchers identified it as a fractured hyaloclastite, a sort of volcanic rock that forms when molten material erupts into the water, shattering into glassy fragments which settle on the seabed. In this case, it was repeatedly heated and cooled by multiple eruptions at the “baked margin” of the Nootka seamount, causing the rock to fracture in block-like patterns. Hyaloclastite is common enough in high-energy underwater eruptions, but the exact geometry here is unusual, making it impressive evidence of how geological processes can take forms that may remind one of human architecture.
Yet findings of this sort are the exception rather than the rule, for the simple reason that so little of Earth’s deep seafloor has ever been seen directly. By definition, the deep ocean comprises waters deeper than 200 meters; it covers 66 percent of the planet’s surface. And yet, by 2025 – according to a global survey of deep-submergence records – humans have visually explored only between 0.0006 and 0.001 percent of the deep seafloor, about 3,823 square kilometers, an area slightly larger than Rhode Island. Thus, 99.999 percent remains unseen.
These have yielded very minute coverage, given the logistic and financial burdens associated with deep-sea exploration. Several millions of dollars are used to work with an ROV or human-occupied submersible at depth on visual surveys of a few square kilometers. The efforts have been ongoing for decades, with most dives having taken place in shallower waters within the Exclusive Economic Zones of a small number of high-income countries. In fact, more than 97% of all deep-sea visual records originate from the US, Japan, New Zealand, France, and Germany, with large swaths of the high seas-and with them many geological wonders-remaining poorly documented.
The “yellow brick road” was discovered out of capabilities granted by modern ROVs like Nautilus’ Hercules, which sport high-definition cameras, manipulator arms, and sampling gear. Such modern vehicles can hover precisely over rough terrain, pipe live video to onshore scientists, and fetch rock samples for laboratory analysis. For the case of Liliʻuokalani Ridge, the telepresenceenabled mission let researchers and the public alike witness the moment of discovery in real time-the outreach potential of deep-sea technology.
Geologically, these formations are a valuable key to submarine volcanic history. Hyaloclastite deposits contain information on the interaction of magma and seawater at high pressure, including eruption temperatures and cooling rates, even the succession of volcanic events. Other studies of oceanic islands-for example, La Palma in the Canary Islands-have mapped and interpreted submarine felsic formations to reconstruct early stages in island growth. Here, trachytic lobe–hyaloclastite complexes-representing viscous, silica-rich lava flow activity-represent the last stages of submarine shield volcano evolution prior to the onset of basaltic volcanism. These deposits will help to understand better the evolution of magma, fractional crystallization processes, and the tectonic setting of volcanic chains.
Such detailed underwater geological mapping has seldom been done; hence, it outlines the need for its extension. According to the researchers, smaller and less expensive AUVs and ROVs should be developed to democratize deep-sea research, particularly for lowand middle-income countries. More diversity among operators, with a decided focus on under-explored geomorphological features-such as abyssal plains and seamount flanks-may reveal thousands of unknown structures, ecosystems, and mineralogical records.
For the moment, the “road to Atlantis,” as one Nautilus team member joked, remains both a scientific curiosity and a symbol of how much is still hidden beneath the waves. Every fracture in that gold-colored rock serves as a reminder that Earth’s largest ecosystem remains a mystery, and that the next big find could be lying just beyond the limits of our present charts.
