They have produced the largest basalt flows on the continents. These eruptions can be from either vents or fissures. The third basalt-forming environment is a continental environment where a mantle plume or hotspot delivers enormous amounts of basaltic lava through the continental crust and up to Earth's surface. Over 300 individual flows have been identified, and several hundred meters of basalt underlies much of the area shown in the map above. The area shown is what has not yet been eroded away - the original extent of these basalt flows was much greater. Public domain image by Williamborg.Ĭolumbia River Flood Basalts Map: A map of the area underlain by the Columbia River Flood Basalts in Washington, Oregon, and Idaho. Although basalt is typically a dark black rock, it often weathers to a yellow-brown color similar to the rocks shown here. The outcrops in the foreground and in the distance of this photo are all made up of layered basalt flows. These flows have travelled over seven miles to reach the ocean, covering highways, homes and entire subdivisions that were in their path.Ĭolumbia River Flood Basalts: The Columbia River Flood Basalts are an extensive sequence of stacked lava flows that reach a cumulative thickness of up to 6000 feet. Basalt flows from Kilauea have extruded over one cubic mile of lava, which currently covers about 48 square miles of land. It has been in amost continuous eruption since January, 1983. Kilauea is the most active of these volcanoes. Today it consists of five overlapping volcanoes. About 100,000 years ago it is thought to have grown tall enough to emerge from the ocean as an island. The volcanic cone grew as recurrent eruptions built up layer after layer of basalt flows. It began as an eruption on the floor of the Pacific Ocean. The island that we know today as "Hawaii" is thought to be between 300,000 and 600,000 years old. All of the islands in the Hawaiian Island chain were built up from basalt eruptions on the sea floor. If the hotspot is sustained, repeated eruptions can build the volcanic cone larger and larger until it becomes high enough to become an island. These submarine fissure eruptions often produce pillow basalts as shown in the image on this page.īasalt production at these locations begins with an eruption on the ocean floor. This hot rock melts as the divergent boundary pulls apart, and the molten rock erupts onto the sea floor. Here convection currents deliver hot rock from deep in the mantle. Most of Earth's basalt is produced at divergent plate boundaries on the mid-ocean ridge system (see map). The lava in these flows originated from the Pu'u'ō'ō vent. A volcanic plume from the Pu'u'ō'ō vent can be seen over the horizon near the center of the image. They extend from the shoreline up to the horizon. This photo shows the enormous extent of the flows. Multiple locations where hot lava streams into the ocean can be seen in this image along with a red-hot lava flow traversing the lava field. Hawaii Basalt Flows: Lava flows dump into the Pacific Ocean on the coast of Hawaii. This lava flow, produced by a fissure eruption, was about five years old when the photograph was taken. Sea floor pillow basalts on the Juan de Fuca Ridge, a divergent plate boundary located about 150 miles (240 kilometers) west of the Washington-Oregon coast. Younger basalt flows will have fewer craters. The ages of lunar maria can be estimated by observing the density of impact craters on their surface. These areas of the Moon are known as "lunar maria." Large areas of the Moon have been resurfaced by extensive basalt flows which may have been triggered by major impact events. Much of the Moon's surface is underlain by basaltic lava flows and flood basalts. Basalt on Moon and Marsīasalt is also an abundant rock on the Moon. Although basalt is much less common on continents, lava flows and flood basalts underlie several percent of Earth's land surface. Most areas within Earth's ocean basins are underlain by basalt. Earth's Most Abundant Bedrockīasalt underlies more of Earth's surface than any other rock type. It is about 375 miles (600 kilometers) in diameter and 15 miles (25 kilometers) high. Olympus Mons is the highest topographic feature on Mars and is the largest known volcano in our solar system. Olympus Mons Volcano: This shield volcano is composed of basalt and has enormous calderas at the summit.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |