Scientists may have finally cracked the recipe behind Venus’ giant pancakes.
Venus is famous for its “pancake domes” — steep-sided volcanoes that rise from the planet’s surface like circular welts. A study now suggests that these unusual dome-shaped structures are at least partly sculpted by the planet’s upper crust, which seems more flexible in certain regions.
Volcanoes are common across Venus, with more than 1,600 large volcanoes or volcanic features discovered so far. One of the more intriguing types are the so-called pancake domes, disk-shaped structures that stretch over tens of miles but are only half a mile in height, like a flattened version of Hawaii’s Mauna Loa.
Exactly how these volcanoes form — and what they’re made of — is still a mystery. One idea is that they develop from super-sticky, slow-flowing lava that moves under the force of its own weight (the technical term for this phenomenon is a viscous gravity current). Eventually, the lava stops moving and solidifies, forming the pancake domes.
But does the domes’ formation depend only on the type of lava? Probably not, Madison Borrelli, a postdoctoral researcher at the Georgia Institute of Technology and first author of the new study, told Live Science by email. One factor that many previous studies hadn’t considered was the bendiness’, or the flexure, of Venus’ upper crust.
It turns out that Venus’ surface — and Earth’s — behaves, in certain areas, like an orange’s skin: under a sufficiently heavy load, the surfaces dimple. If such dimpling accompanied the pancake domes’ formation, it would leave certain tell-tale signs, like a bulge surrounding the dome, where the crust buckled upwards. Indeed, a 2021 study found such flexural signatures surrounding one-fifth of a sample of Venusian pancake domes.
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To determine how a bendy crust could affect the formation of a pancake dome, Borrelli and her colleagues at universities in France and the U.S. focused on the only dome for which they had high resolution data: the Narina Tholus, an 88.5-mile-wide (55 kilometers) dome located on the circumference of the Aramaiti Corona, one of the many giant oval structures that pockmark Venus’ surface.
The new study, published May 10 in the Journal of Geophysical Research: Planets, used topographical data collected by NASA‘s radar-wielding Magellan mission in the 1990s, the researchers created a virtual model of the Narina Tholus dome. They then simulated viscous gravity currents of lavas of different densities atop both a flexible upper crust and a rigid lithosphere, and compared the results to the virtual dome.
The study’s results showed that domes created on a bendy crust looked far more like the virtual pancake dome than those that formed on the rigid lithosphere. In particular, the flexible crust’s domes had flat tops and very steep sides, characteristic of the pancake domes. This stems from the fact that the bulge around the dome prevents the lava from flowing further, causing it to accumulate, the researchers said. The bendy lithosphere’s domes also had flexural signatures similar to that of Narina Tholus.
However, the dimpling of the lithosphere couldn’t alone explain the domes’ features — the lava’s density mattered too. Although low-density lavas produced domes with the right sort of shape, they created smaller crustal bulges than those found near the real-life pancake dome. Only lavas denser than 0.0867 lbs per cubic inch (2,400 kg/m3) — or over twice the density of room temperature water — produced both the correct dome shapes and flexural signatures. These high-density lavas were more than a trillion times as viscous as ketchup at room temperature and settled down to form the domes over hundreds of thousands of Earth-years.
Nonetheless, the study’s main drawback is that it used data from just the Narina Tholus dome. Borrelli hopes that upcoming missions to Venus — like NASA’s VERITAS program — will provide higher resolution topography of the planet’s surface, allowing the researchers to test their model with more data.
The new data could also help determine the exact type of lava that forms the pancake domes, a question the researchers were unable to answer. While most Venusian volcanoes appear to spew Mauna Loa-like basaltic lava, the researchers couldn’t rule out rhyolitic and andesitic lavas, similar to those that spout from Mount St. Helens.
Borelli said that finding diverse lava types on Venus would be interesting. “This can tell us about the planet’s tectonic history, magmatic processes, and even the potential past presence of water.”
