Geology of Thalassa

The geology of Thalassa was created based on real-world examples of planetary dynamics on Earth and other planets, especially Mars. Here I present the research concepts I used to create the geology, geography, and oceanography of the planet. To begin, let’s travel back in time about 100 million years ago to the planet Thalassa…
Source: esciencework

At that time the planet had a hot, molten inner core that supported active continental drift across the planet. Oceanic plates, driven by underwater spreading centers in the middle of the ocean, created collisions with other plates and subsequent subduction zones with deep-sea trenches. As ocean seafloor was subducted below the surface it created molten magma which rose to the surface creating an active chain of volcanoes. Over time, these volcanoes created islands, which were the forebears of the western chain of islands off Thalassa’s continent.

But small planets like Thalassa, which is only 10% the mass of Earth, cool rapidly. Without internal heat to drive tectonics, plate movement ceases, the planet’s core cools, and it loses its magnetic field. In the absence of this protective field, solar wind boils off the atmosphere and then the ocean. This process is accelerated on Thalassa as it is a smaller planet with less gravity to hold on to its air and water. This happened on Mars three billion years ago, which is why it is largely a dead planet. Before that time it had extensive oceans covering its surface.

Island arc formation showing erosion as the islands age without renewed volcanism. Source:
My vision of what Thalassa’s island would look like. Source: Visuals Unlimited/Corbis.

But over time, in the absence of continued volcanism, the line of islands was eroded into the sand and rocky cores of the islands the Duke mission discovered on their journey. Because they were formerly volcanic, the rocky cores had lava tubes both above and below the water which served as caves for the Nesoi.

Rise of the Bulge

As plate tectonics on Thalassa ceased, residual heat in the planet’s core pushed magma to the surface. But in the absence of plate movement, instead of a string of islands, volcanism created a large, stationary volcano that became the bulge. The idea for a giant shield volcano on Thalassa is modeled after mound volcanoes on the Tharsis Bulge on Mars such as Olympus Mons.

The contrast between volcano formation on earth (with plate tectonics) and Mars (without).
Olympus Mons on Mars. the largest volcano in the solar system. Photo: NASA.

The bulge, however, is different from Tharsis volcanoes in three important ways. One, the bulge is smaller, only 25-30 miles across while volcanoes on Mars range from 43-370 miles across. Second, after it was formed and volcanism stopped, wind and rain eroded the bulge forming canyons because Thalassa still had an atmosphere (and weather). Third, as sea levels rose the bulge was covered with water and canyons became submarine canyons; the perfect condition for large waves.

When the team arrived in 2090 they discovered the geological processes of volcanism and erosion had created the perfect surfing spot. As in the book, two submarine canyons formed in proximity to a thumb-shaped reef Milo named Colossus. Based on Nazaré Portugal, one of the top big wave surf spots in the world, Colossus is a rocky reef surrounded by two submarine canyons. The waves move fast in the deep water and are focused by the submarine canyon walls where they focus their energy, along with the incoming swells, up on a sharp, jagged reef to create monster waves. This tripling of swell energy results in waves over 150 feet.

Rogue Planet

But after the formation of the islands and the bulge, volcanism ceased for 50 million years. And if nothing changed Thalassa would have gone the way of Mars and become a dead planet. But 10 million years ago, an event happened that had a profound effect on the future of Thalassa. Something, perhaps a star-less rogue planet ejected from a distant solar system, moved through the Procyon system and was captured as Thalassa’s second moon — Hina. The new satellite developed a highly elliptical orbit around the planet that cast it far out in space and then perilously close to the planet over a two-year period, causing havoc on the planet. Significantly, it created a renewal of volcanism on Thalassa a new line of volcanoes.

Geological Terrain of Thalassa

Given its volcanic origins, I based the description of Thalassa’s continent on volcanic landforms in Hawaii, the Canary Islands, and other locations around the world. Here are a few to help you imagine the landscape of Thalassa.

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