How do volcanoes create new land on islands and coastlines?

When lava erupts underwater or near the coast, it can cool quickly and accumulate into thick layers of rock. Repeated eruptions build volcanic cones and shield volcanoes that eventually rise above sea level. The Hawaiian Islands are a famous example of volcanic island building over millions of years. In the 1960s, the Surtsey eruption off Iceland created a new island that scientists still study today. In some places, lava flows can also extend the coastline by adding land directly into the ocean.