At a given latitude, the magnetic inclination is always the same. The largest island in these Windward Islands is Dominica, with an area of 750 km 2 or 290 sq mi. It turns out that some of the answers can be pieced together from the effects glacial episodes have had on the Hawaiian Islands. On the average it takes about 1. Farallon de Medinilla - … 0. The two line solution suggests that recently tectonic motion has slowed somewhat with respect to rates prevalent in the Pacific more than 30 million years ago. Ages of some of the Hawaiian Islands and outer seamounts Volcano Number see note at table bottom Volcano Name Distance from Kilauea along trend of chain km Best K-Ar age Ma Data Source tabulated below 1 Kilauea 0 0-0.
Current ocean floor beneath Hawaii was constructed at the Mid-Pacific rise just off the west coast of the Americas. Over the last 65 million years, about 1 million cubic kilometers of lava has been produced. As the magma reaches the surface, it cools quickly and forms pillow lava. It is over 30,000 feet tall from the seafloor where it was born to the summit, which is 13,684 feet above sea level. The next image on the left shows the situation about 56 million years ago.
It even snows at upper elevations here on the mountain tops. There is another Windward Islands that is used to refer to the southeastern part of the Hawaiian Islands. Explain the origin of these features. If you have comments or suggestions, email me at. This process is repeated continuously as long as the plates remain in motion and the hot spot remains active. This curve would indicated a small but significant slowing of plate velocity over the past 70 million years, a result that seems reasonable as the heat driving plate motion is slowly lost to space. Morgan suggested a large amount of excess energy was welling up from deep within the planet.
The bowing of the crust in the vicinity of the active end of the chain is shown in cross section on the figure on the right. Saito and Ozima 1977 9. The aging of the islands with distance from the current hot spot is demonstrated in the diagram below, where distance along the chain is approximated as distance away from Kilauea volcano the youngest above-sea-level Hawaiian volcano. How does a caldera form? This image shows the configuration when the oldest volcanoes that still exist today were just being formed. The fact that about half of the volcanoes mass lies beneath the level of the ocean crust would roughly double the measure volumes to about 2 million cubic kilometers. There has been much speculation regarding the cause for this bend.
Main eruptive vents are shown as stars. What do you notice about the lines of island groups in the Pacific Ocean? Tinian - 101 km 2. Dalrymple and others 1981 21. It fills the deepest part of the trough caused by the down bowing of the lithosphere, which is roughly 80 kilometers thick. The Hawaiian Island chain indicates that the plate moved 10 cm per year. It began to break the surface of the Pacific Ocean about 4.
A geologist in the 1960's, by the name of Tuzo Wilson, noticed that there were straight lines of submarine volcanoes and volcanic islands in the Pacific. The answer is radiogenic dating. The rising mantle plume causes crustal material to melt at depth, which results in volcanism and finally in the formation of a volcanic island. Morgan proposed that there are 20 different hot spots in the world. At the end of an ice age, the volcanoes continue to sink as sea level rises, exterminating the coral.
The important component is the angle from the horizontal, known as the magnetic inclination. In effect, known the inclination of the magnetic field of a lava sample tells you the latitude at which it cooled and solidified. Garcia and others 1986a 11. Since there is no such hole, there must be some mechanism to replace the material lost and erupted to the surface. This, together with flexure of the plates produces a rise paralleling the island on both sides known as the Hawaiian Rise. The most well-known is in the south of the Caribbean.
Two lines fit the data somewhat better, as will always be the case. Over time however, the tectonic plate that the island is on will move and the area will no longer be on top of the hot spot and it will slowly wither away. Northwest of Midway Island there is an elbow bend in the Hawaiian-Emperor Seamount Chain of Islands that implies something about Pacific plate movement through time. The eruption rate for Hawaiian volcanoes has remained quite constant over most of the 65 million years of preserved activity. By contrast, tide guage data from Oahu, which has ceased growing and is therefore stable, shows very little evidence for continued subsidence. Mountains of Fire: The Nature of Volcanoes.
As far as European exploration goes, however, the Hawaiian islands were not discovered until Captain James Cook came across them in 1778. This indicates that the magma used in hot spots comes from a deeper source than volcanoes at plate boundaries. Whatever the cause, it is clear that there was a massive reorganization of plate motion nearly 50 million years ago. This pillow lava rests on the contact edges of the volcano growing quickly as magma. Their geometry provides a key to the direction s and rate s of movement of the Pacific Plate over a stationary hotspot.
As a rock ages, from the time it solidifies, argon atoms slowly build up, trapped in the crystal lattice, while the amount of unstable potasium slowly decreases at a very uniform, and predicitable rate. The result is that if the island is sinking, the sea level appears to rise. It is an amazing concept that a piece of land is located out in the middle of a large ocean. Instead long linear chains of islands form as the Pacific plate moves over the Hawaiian Hotspot. This ridge has since been subducted beneath Alaska, but then it was actively making oceanic lithosphere. The trend continues with the image on the right. Porter and others 1977 12.