Geomorphological features of the seamounts in the hadal trenches based on collaborative observations of shipborne multibeam bathymetric data and "Fendouzhe" Full-ocean-depth Manned Submersible

Seamounts are one of the core structural units that shape the complex topography of trenches, serving as key conduits for material-energy exchange between Earth′s deep interior and shallow crust. Current research on seamounts geomorphology within the hadal trenches remains relatively underdeveloped, with significant deficiencies in underwater in-situ observations. Based on multi-sources topographic data primarily from shipborne multibeam data and observations from the "Fendouzhe" Full-ocean-depth Manned Submersible, this paper extracts and statistically analyzes the morphological parameters of seamounts within the Java Trench (Indian Ocean), the Kuril-Kamchatka Trench (northwestern Pacific Ocean), and the Kermadec Trench (southwestern Pacific Ocean). We find that the seamounts in the Java Trench and Kermadec Trench are predominantly near-circular and elliptical while most seamounts in the Kuril-Kamchatka Trench are elongated. The average values of width-to-height ratio, flatness, and average slope angles of seamounts in the Kuril-Kamchatka Trench are higher than those in the Java Trench and Kermadec Trench. High-resolution images from submersible-mounted cloud camera systems reveal in-situ lithological distinctions of seamounts: predominant yellow-brown rocks in the Java Trench and Kuril-Kamchatka Trench versus black rocks in the Kermadec Trench. Integrating previous research findings, this paper proposes that the differences in the morphology of seamounts within three trenches are mainly influenced by a combination of external factors, including tectonic environments and magmatic sources during seamount genesis, pre-existing fractures/faults on the subducting plates, and sediments thickness covering on the seamounts. The morphological evolution of the seamounts within the three trenches has the characteristics of simultaneously top aggradation and lateral progradation. Among them, the seamounts in the Kuril-Kamchatka Trench primarily exhibit top aggradation, while those in the Kermadec Trench mainly show lateral progradation of edifice flanks. These finds provide novel analytical pathways for revealing the typical topographic and geomorphological features of subduction-type hadal deeps, offering critical insights for research on the mechanism of seamounts subduction, earthquake hazards assessment, and analysis of the benthic habitat′s environment in hadal deeps.