Kīlauea's high state of activity has a major impact on its mountainside ecology, where plant growth is often interrupted by fresh tephra and drifting volcanic sulfur dioxide, producing acid rains particularly in a barren area south of its southwestern rift zone known as the Kaʻū Desert. Nonetheless, wildlife flourishes where left undisturbed elsewhere on the volcano and is highly endemic thanks to Kīlauea's (and the island of Hawaiʻi's) isolation from the nearest landmass. Historically, the five volcanoes on the island were considered sacred by the Hawaiian people, and in Hawaiian mythology Kīlauea's Halemaʻumaʻu served as the body and home of Pele, goddess of fire, lightning, wind, and volcanoes. William Ellis, a missionary from England, gave the first modern account of Kīlauea and spent two weeks traveling along the volcano; since its foundation by Thomas Jaggar in 1912, the Hawaiian Volcano Observatory, located on the rim of Kīlauea Caldera, has served as the principal investigative and scientific body on the volcano and the island in general. In 1916, a bill forming the Hawaii Volcanoes National Park was signed into law by President Woodrow Wilson; since then, the park has become a World Heritage Site and a major tourist destination, attracting roughly 2.6 million people annually.