Read this excerpt from "Types of Volcanoes." Shield volcanoes can grow to be both several miles wide and several miles tall. The Hawaiian Islands are a string of shield volcanoes rising high above the ocean floor. One of those shield volcanoes, Mauna Loa, is the world’s largest active volcano, rising 28,000 feet above the ocean floor and 13,677 feet above sea level. A shield volcano is built up over long periods of time as layers of lava flow down the sides and solidify on top of old layers. Lava escapes from the top of the volcano summit either through one vent or a group of vents.

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Based on size and structure, there are basically four different kinds of volcanoes.
A volcano is built up around a vent in the ground where magma from inside the Earth escapes above ground.
Volcanoes that develop over a long time to be many miles wide and tall are called shield volcanoes.
Hawaii is a US state built on volcanoes that rise out of the Pacific Ocean.