It’s enough to make you forget the ice age outside. The theory is this lava is coming up from great depths in the shelves of the earth. How deep? Well here, The Mariana Deep is seven miles below sea level and it hasn’t penetrated the shelf enough to go ballistic.
The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovicic discontinuity, a boundary defined by a contrast in seismic velocity. The crust occupies less than 1% of Earth’s volume.
The crust of the Earth is of two distinctive types: oceanic and continental. The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust.
Both the continental and oceanic crust “float” on the mantle. Because the continental crust is thicker, it extends both to greater elevations and greater depth than the oceanic crust. The slightly lower density of felsic continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, water runs off the continents and collects above the oceanic crust. Because of the change in velocity of seismic
As the top of the continental crust reaches elevations higher than that of the oceanic, water runs off the continents and collects above the oceanic crust. Because of the change in velocity of seismic waves it is believed that beneath continents at a certain depth continental crust (sial) becomes close in its physical properties to oceanic crust (sima), and the transition zone is referred to as the Conrad discontinuity. The temperature of the crust increases with depth, reaching values typically in the range from about 200 °C (392 °F) to 400 °C (752 °F) at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere. Because of convection in the underlying plastic (although non-molten) upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C (54 °F) for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust.
The temperature of the crust increases with depth, reaching values typically in the range from about 200 °C (392 °F) to 400 °C (752 °F) at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere. Because of convection in the underlying plastic (although non-molten) upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C (54 °F) for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust.
Plates in the crust of Earth
Partly by analogy to what is known about the Moon, Earth is considered to have differentiated from an aggregate of planetesimals into its core, mantle and crust within about 100 million years of the formation of the planet, 4.6 billion years ago. During the Hadean, the primordial crust was very thin and was probably destroyed by much more vigorous plate tectonics, volcanic activity and significant asteroid impacts, which were much more common in the early stages of the solar system.
Earth has probably always had some form of basaltic crust, but the age of the oldest oceanic crust today is only about 200 million years. In contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4.28 billion years [and have been found in the Narryer Gneiss Terrane in Western Australia, in the Acasta Gneiss in the Northwest Territories on the Canadian Shield, and on other cratonic regions such as those on the Fennoscandian Shield. Some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane.
The average age of the current Earth’s continental crust has been estimated to be about 2.0 billion years. Most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth and so are not readily destroyed by subduction.
Formation of new continental crust is linked to periods of intense orogeny; these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms in part by aggregation of island arcs including granite and metamorphic fold belts, and it is preserved in part by depletion of the underlying mantle to form a buoyant lithospheric mantle.
Assuming the molten core of the earth is relatively similar worldwide the lava pouring forth in Hawaii originally began more than 6407 kilometers beneath the surface and it has retained its heat every inch of the way.
What makes molten lava erupt from Mount St. Helena and not spring forth from a much lower depression 20 miles away? There must be nine switches in times that are past decisions to go this way, that way, or Callowaye to come out at a specific point repeatedly. Is there a secret hollow passageway under the volcanoes? Or is there a cheap batch of dirt that winds all down to the core and melts at the first sign of planetary malcontent?
Indonesia has many volcanoes and earthquakes because of its geographical position. The archipelago that starts in Northern Sumatra stretches over 3,000 miles south. It has been created by the forces where two of the tectonic plates that make up the Earth’s surface, meet. The ocean floor of the Indo-Australian Plate and the Asian landmass of the Burma Plate are in collision. As they push against each other the heavier ocean floor yields the match and is forced underneath the lighter continental rock. Krakatoa lies directly above this subduction zone and Taiwan isn’t far off center.
Why does the land under the ocean weigh more? Let’s go the other weigh first. When I was 7 years old (69 years ago) my father showed this principle to me. He took an old rusty stove pipe and clenched it 3 feet deep and angled it across the road where heavy trucks rolled. “The deeper you put it the more weight that stove pipe can carry without bending.”
Water, on the other hand, gains weight as you go down. For every cubic foot of water above your head the water gains another 8 pounds. Eight pounds? That’s about the weight of two human brains. That is some heavy thinking dude.
All the information contained in this article comes directly from Wikipedia. I found the information by going to Google!