Constraining the Long-Term Tectonic Uplift Rate of Araki, Vanuatu using Coralline Algae

Abstract

Araki is an island in the Republic of Vanuatu in the South Pacific Ocean between Fiji and New Caledonia. This island lies on the convergence of two major tectonic plates, the Australian Plate and the New Hebrides Plate. This feature makes this area one of the most tectonically active places on the planet. As a result of the collision, Araki initially subsided and is now uplifting. Coral terraces surround the island, and as it uplifts, fossil coral terraces are left behind. Coralline algae grow on some corals, forming branches or crusts on the coral surface. A specific crustose species, Porolithon onkodes, is restricted to the upper three meters of water. Its presence in the fossil coral record indicates shallow water at the time of growth. In 2019, Dr. Christina Gallup went to the island to collect samples of these fossil corals and associated coralline algae along the uplifted terraces from the summit to the bottom of the island. In 2022, previous undergraduate honors student Rayann Rehwinkel dated the samples from the summit of the island. Using these dated samples, and the presence of Porolithon onkodes, a new long-term uplift rate can be determined, revealing a more refined tectonic history of Araki.