Recent studies have shown that explosive volcanic activity can occur even deep underwater, contrary to early assumptions that high water pressure would prevent it. Observations at sites like West Mata and NW Rota-1 volcanoes in Tonga’s NE Lau Basin reveal that underwater eruptions can produce volcanic fragments (pyroclasts and hydroclasts) through several processes, including explosions inside the vent, contact with seawater, and rapid cooling. These events create thick deposits near the vent and finer layers that spread far away. Research cruises between 2009 and 2018 in Tonga’s NE Lau Basin found widespread volcanic deposits, with layers of ash and debris up to 2 meters thick covering lava flows. These deposits shape seafloor landscapes, contribute to slope instability, and influence local ecosystems. Despite the challenge of collecting samples due to the mix of very coarse and very fine materials, scientists can use special tools to recover specimens to analyze particle size and shape. Findings suggest that both direct eruption deposits and later underwater transport processes play roles in how these materials are distributed.