Passage: The islands are part of a geologic structure known as the Izu-Bonin-Mariana Arc system, and range in age from 5 million years old in the north to 30 million years old in the south (Guam). The island chain arose as a result of the western edge of the Pacific Plate moving westward and plunging downward below the Mariana plate, a region which is the most volcanically active convergent plate boundary on Earth. This subduction region, just east of the island chain, forms the noted Mariana Trench, the deepest part of the Earth's oceans and lowest part of the surface of the Earth's crust. In this region, according to geologic theory, water trapped in the extensive faulting of the Pacific Plate as serpentinite, is heated by the higher temperatures of depth during its subduction, the pressure from the expanding steam results in the hydrothermal activity in the area and the volcanic activity which formed the Mariana Islands.All the islands, except Farallon de Medinilla and Uracas or Farallon de Pajaros (in the northern group), are more or less densely wooded, and the vegetation is dense, much resembling that of the Carolines and also of the Philippines, from where species of plants have been introduced. Owing to the moistness of the soil cryptogams are numerous, as are also most kinds of grasses. On most of the islands there is a plentiful supply of water.

Question: What is in abundance on most islands?
supply of water