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Seafloor Spreading, Part 2

© Geoff Habiger

In the late 1920's a Dutch scientist, Venig Meinesz, conducted research on gravity anomalies around the area of the Java Trench. The Java Trench hugs the southern coasts of Java and Sumatra. Here the ocean floor drops for thousands of feet to a depth of nearly five miles. Meinesz's research showed that in the area around the Java Trench there was a lowering in the strength of the local gravitational field. In 1939 Meinesz teamed up with Harry Hess and two other scientists to conduct research in the Caribbean. Their research showed similar gravity anomalies in the trenches of the Caribbean as were found around the Java Trench. Hess wrote in 1939:

"...an important new concept concerning the origins of the negative strip of gravity anomalies...has been set forward...It is based on model experiments in which... convection currents were set up in a fluid layer beneath the "crust" and a convection cell was formed. A down-buckle in the crust ...was developed where two opposing currents meet and plunge downwards."

Already Hess had developed the core of his idea that would lead to the seafloor spreading theory. But his theory was still 23 years away from being realized and would require two more cornerstones researched by other scientists. Two cornerstones had already been realized, the age of the ocean floor was younger than first believed (no older than Late Jurassic in age), and the discovery of magnetic anomalies in the ocean crust that were tied to the reversals of the Earth's magnetic field. Two other cornerstones would seal the evidence in favor of Hess's hypothesis.

Hawaiian Islands
The Hawaiian Islands are located thousands of miles from any region of high earthquake or volcanic activity yet the Islands owe their existence to volcanism. The Islands are the located over a geologic hot spot, a spot on the Earth where the hot magma in the mantle pushes up through the lithosphere to erupt on the surface. The Earth is dotted with hot spots, most are not as well known as the Hawaiian Islands.

The Hawaiian Islands consist of more than the rocks that jut from the sea at the southeast tip of the island chain. From the island of Hawaii the chain stretches for more than 2,500 miles across the Pacific Ocean. The islands age as they travel to the northwest, a fact that was known to the ancient Polynesians that colonized the islands. The age of the islands was incorporated into the legends of the Hawaiian gods. Pele, the goddess of volcanoes, once lived on the island of Kauai. Pele's older sister, Namakaokahai, the goddess of the sea, attacked Pele who fled to Oahu. Namakaokahai attacked again and Pele fled to the southeast again to Maui. Pele's sister attacked a third time and Pele fled again to Hawaii where she resides today. Each island Pele fled from was older than the next island in the chain.

Diagram of convection cells in the Earth.

Hawaiian Island chain.

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