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Panum Crater is between 600 and 700 years old, and it exhibits all of the characteristics of the textbook rhyolitic lava dome. Rhyolitic volcanoes are characterized by having large amounts of silica (quartz) in their lava. The content of silica at Panum is about 76 percent. It makes the lava very viscous, or thick, and very glassy.
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one meter in diameter. They form the upper part of Layer 2 of ...
Pillow lava is the lava structure typically formed when lava emerges from an underwater volcanic vent or subglacial volcano or a lava flow enters the ocean. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow.
Stratovolcano. Mount Rainier, a 4,392 m (14,411 ft) stratovolcano, the highest point in the US state of Washington. Exposed internal structure of alternating layers of lava and pyroclastic rock in the eroded Broken Top stratovolcano in Oregon. A stratovolcano, also known as a composite volcano, is a conical volcano built up by many alternating ...
This eruption took place underwater, [83] and it produced viscous lava that created a rhyodacite lava dome, about 2,400 years after the first period of postcaldera activity. [87] Given that Mazama has had periods of sporadic eruptions for 420,000 years, the United States Geological Survey thinks that it is "virtually certain" that Mazama will ...
The tendency of felsic lava to be cooler than mafic lava increases the viscosity difference. The silicon ion is small and highly charged, and so it has a strong tendency to coordinate with four oxygen ions, which form a tetrahedral arrangement around the much smaller silicon ion. This is called a silica tetrahedron. In a magma that is low in ...
The Mount Edziza volcanic complex is a linear group of volcanoes in northwestern British Columbia, Canada. [8][9] It is about 65 kilometres (40 miles) long and 20 kilometres (12 miles) wide, consisting of several stratovolcanoes, shield volcanoes, subglacial volcanoes, lava domes and cinder cones. [8][10][11] This volcanic complex includes a ...
When the viscous lava flow encounters a surface, friction drags the mobile lava and forms internal banding. [36] Structureless hyaloclastite is commonly found in Archean felsic volcanic rocks. [7] [17] [36] [37] In submarine environments, water quenches and cools lava rapidly during volcanic eruption. [7]