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The greater the viscosity, the greater the tendency for eruptions to be explosive rather than effusive. As a result, most lava flows on Earth, Mars, and Venus are composed of basalt lava. [36] On Earth, 90% of lava flows are mafic or ultramafic, with intermediate lava making up 8% of flows and felsic lava making up just 2% of flows. [37]
Markagunt Plateau. Markagunt Plateau is a volcanic field in southern Utah, United States. Formed in a region of older volcanics, it consists of several cinder cones and associated lava flows. Some of the lava flows feature lava tubes such as Mammoth Cave, while others have formed lava dams and lakes like Navajo Lake.
The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class. [9] Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava.
Effusive eruptions involve a relatively gentle, steady outpouring of lava rather than large explosions. They can continue for years or decades, producing extensive fluid mafic lava flows. [43] For example, Kīlauea on Hawaiʻi continuously erupted from 1983 to 2018, producing 2.7 km 3 (1 cu mi) of lava covering more than 100 km 2 (40 sq mi). [44]
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate ...
The Sister's Peak region in northwest Ascension has intermediate mafic lava flows, scoria cones and mafic ash fall deposits near Long Beach. The flows formed approximately 829,000 years ago and range between basalt, hawaiite and mugearite compositions. Benmoreite flows outcrop near Long Bay and west of Lady Hill. Additionally, benmoreite cinder ...
Another process is magma mixing between felsic rhyolitic and mafic basaltic magmas in an intermediate reservoir before emplacement or lava flow. [50] If the erupted magma contains <52% and >45% silica, the lava is called mafic (because it contains higher percentages of magnesium (Mg) and iron (Fe)) or basaltic. These lavas are usually hotter ...
The mafic shield-building stage 14.9 to 6.9 million years ago began with the eruption of thin mafic lava flows over an erosion surface. [5] Successive eruptions sent lava pouring in all directions from central vents, forming a broad, gently sloping volcano of flat, domical shape, with a profile much like that of a warrior's shield.