<P> Yellowstone National Park spans an area of 3,468.4 square miles ( 8,983 km ) , comprising lakes , canyons , rivers and mountain ranges . Yellowstone Lake is one of the largest high - elevation lakes in North America and is centered over the Yellowstone Caldera , the largest supervolcano on the continent . The caldera is considered an active volcano . It has erupted with tremendous force several times in the last two million years . Half of the world 's geothermal features are in Yellowstone , fueled by this ongoing volcanism . Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone . The park is the centerpiece of the Greater Yellowstone Ecosystem , the largest remaining nearly - intact ecosystem in the Earth 's northern temperate zone . In 1978 , Yellowstone was named a UNESCO World Heritage Site . </P>
what formed the central portion of yellowstone national park about two million years ago
the Yellowstone Caldera , the largest supervolcano on the continent