Mid-oceanic ridges, where plates spread apart
Subduction zones, where plates collide and one dives under the other (subducts)
Hot spots, where a plume of molten material appears in the middle of a plate.
Next, the land
It’s believed that the Hawaiian Islands exist where the Pacific Plate, on which they ride, is moving northwest across a hot spot. An undersea volcano is built at the place where the plate is over the hot spot. If the volcano gets big enough, it breaks the ocean’s surface to become an island. Eventually, the plate’s movement carries the island far enough away from the hot spot that volcanism ceases on that island. Erosion, which begins the moment the new island appears above the sea, tears the land down.
Deep valleys surrounded by steep cliffs are typical landforms sculpted by the erosion of Hawaiian volcanoes—here, windward Oahu.
The Hawaiian Islands are successively older toward the northwest and younger toward the southeast. Northwestern islands, like Necker, are hardly more than bits of volcanic rock now. Southeastern islands, including the major Hawaiian Islands, are still significant chunks of land. Kauai and Niihau are the oldest and the farthest northwest of the major islands. Oahu is younger, and Maui is younger yet. The Big Island of Hawaii is the youngest and the farthest southeast of the major islands.
The molten material—lava—characteristic of Hawaiian volcanoes is relatively fluid. The fluidity of the lava allows it to spread widely, and repeated eruptions produce broad-based, rounded volcanoes called shield volcanoes. The volcano expels not only flowing lava but volcanic fragments such as cinder and ash. Alternating layers of these materials build up during periods of volcanic activity.
Erosion has sculpted the exotic landscapes we associate with volcanic tropical islands. Waves pound the volcano’s edges, undercutting them and, where the volcano slopes more steeply, forming cliffs. The cliffs at the extreme west and east ends of Oahu are wave-cut cliffs. These wave-cut cliffs grade into the dramatic, fluted stream-cut cliffs (pali) and lush valleys. Streams take material from higher on the volcano, cutting valleys into its flanks and depositing the material they carry as alluvium. Alluvial deposits cover the floors of the stream-cut valleys. New episodes of volcanism wholly or partly fill in those landscapes, and erosional forces immediately begin sculpting the new surface as well as the remaining older surface.
Oahu is geologically an infant on an Earth more than 4 billion years old. Potassium-argon dating of rocks suggests that lava welled forth to build the Waianae volcano between 3 and 4 million years ago. After three major periods of activity, it finally became quiet about 2.5 million years ago. Since then, erosion has carried away most of it, leaving only a crescent-shaped piece of its east rim standing as the Waianae Range. The Koolau volcano burst forth between 2.6 and 1.8 million years ago, building its shield in a single major period of activity and building up the plateau between the two volcanoes. Now, erosion has worn away most of the volcano’s eastern rim, leaving its long west rim standing as the Koolau Range.
Then, about 1.1 million years ago, a period of secondary, cone-building eruptions began on southeast Oahu. By the time it ended some 31,000 years ago, it had left cones that are some of Oahu’s most famous landmarks: Diamond Head, Koko Head, Koko Crater, and Hanauma Bay, to name a few. Is it all over now? No one can be sure. There is circumstantial evidence that an undersea eruption may have occurred between Oahu and Kauai in 1956. In the meantime, however, erosion prevails on Oahu, changing the landscape constantly.
Life arrives
Living organisms colonize new land rapidly. In Hawaii, plants established themselves once there was a little soil for them. Seeds arrived on the air currents, or floated in on the sea, or hitched a ride on the feathers or in the guts of birds. Insects and spiders also took advantage of the air currents. Birds were certainly among the first visitors. Living things found little competition and quickly adapted to their new home, evolving into an astonishing variety of species many of which occur naturally only on the Hawaiian Islands (“endemic to Hawaii”). The only mammals to arrive were the bat and the seal. Some birds became flightless—a fairly common adaptation on isolated islands with no ground predators.
Cayenne vervain’s blue flowers are a common sight along Hawaiian trails.
Flourishing taro patch (Colocasia esculenta)
People arrive
It’s unlikely that the site of the very first human colony in the Hawaiian Islands will ever be found. Too much time has passed; too many destructive forces have been at work. However, recent archaeological work has established that people had settled in Hawaii by 300–400 A.D., earlier than had previously been thought. Linguistic studies and cultural artifacts recovered from sites of early colonization point to the Marquesas Islands as the colonizers’ home; the Marquesas themselves seem to have been colonized as early as 200 B.C.
The colonizers of Hawaii had to adapt the Marquesan technology to their new home. For example, the Marquesans made distinctive large, one-piece fishhooks from the large, strong pearl shells that abounded in Marquesan waters. There are no such large shells in Hawaiian waters, so the colonists developed two-piece fishhooks made of the weaker materials that were available in Hawaii (such as bone and wood). Over time, a uniquely Hawaiian material culture developed.
At one time, scholars believed that, as related in Hawaii’s oral traditions and genealogies, a later wave of colonizers from Tahiti swept in and conquered the earlier Hawaiians. Research does not support that theory. Instead, research has revealed that before European contact, Hawaiian material culture evolved steadily in patterns that suggest gradual and local, not abrupt and external, influences. The archaeological record hints that there may have been some Hawaiian-Tahitian contact in the 12th century, but its influence was slight.
The Hawaiians profoundly altered the environment of the islands. They had brought with them the plants they had found most useful in the Marquesas Islands: taro, ti, the trees from which they made a bark cloth (tapa or kapa), sugar cane, ginger, gourd plants, yams, bamboo, turmeric, arrowroot, and the breadfruit tree. They also brought the small pigs of Polynesia, dogs, jungle fowl, and, probably as stowaways, rats. They used slash-and-burn techniques to clear the native lowland forests for the crops they had brought. Habitat loss together with competition for food with and predation by the newly introduced animals wrought havoc with the native animals, particularly birds. Many species of birds had already become extinct long before Europeans arrived.
On the eve of the Europeans’ accidental stumbling across Hawaii, the major Hawaiian islands held substantial numbers of people of Polynesian descent. They had no written language, but their oral and musical traditions were ancient and rich. Their social system was highly stratified and very rigid. Commoners, or makaainana, lived in self-sufficient family groups and villages, farming and fishing for most necessities and trading for necessities they could not otherwise obtain. The land was divided among hereditary chiefs of the noble class (alii). Commoners paid part of their crops or catches as taxes to the chief who ruled the land-division they lived on; commoners served their chief as soldiers. Higher chiefs ruled over lower chiefs, receiving from them taxes and also commoners to serve as soldiers. People especially gifted in healing, divination, or important crafts served the populace in those capacities (for example, as priests). There was also a class of untouchables, the kauwa. Most people were at death what they had been at birth.
Strict laws defined what was forbidden, or kapu, and governed the conduct of kauwa toward everyone else, of commoners toward alii, of alii of a lower rank toward alii of higher rank, and of men and women toward each other. Some of the laws seem irrationally harsh. For example, a commoner could be put to death if his shadow fell on an alii.
Chiefs frequently made war on one another. If the chiefs of one island were united under a high chief