Lava domes form when magma rises which is semi molten rock from the crust lithosphere and the asthenosphere It usually occurs after an eruption from the volcano but the eruption must not be an explosion After the magma flows out through the volcano pipe it slows down due to its density and the lava cools on top of the vent of the volcano When it cools on top it produces a bump of hardened rock on top of the vent or caldera which is a bowl like depression in the chamber of a volcano When the lava reaches the surface its consistency is very dense and sticky Its consistency is between a solid and a liquid Since the lava is dense it does not flow down the volcano like a normal eruption The lava stays around the vent as it blocks new lava from coming out If the new lava is persistent enough then the new lava pushing the hardened layer will create cracks and broken debris A mound pops up atop of its surroundings In normal eruptions the lava breaks through the surface but a lava dome forms when the magma slowly rises from under the ground causing a build up of a mound shaped dome Magma bursts out because of pressure and density build up from the mantle It is just a way of the Earth releasing tension and heat
In the plate tectonics theory the Earth's crust is broken down to a series of plates that interact with each other and causes landforms Plates float on the mantle and can diverge split apart converge rams against each other transform slide side by side parallel to each other or subduct to sink under one another Volcanoes form where plates subducts or sinks beneath one another and this causes an opening in the crust This happens near the edge of a plate called a plate boundary where both plates comes in contact with each other As the heavier plate sinks into the mantle the mantle melts the crust and that produces molten rock that we call magma When it reaches the surface it is called lava Magma is less dense than the crust that it holds so whenever there is an opening in the crust magma will rise up As they ascend the gas molecules form bubbles and these bubbles become strong enough to break its surrounding structures The magma in a lava dome typically does not have enough gas or pressure for it to explode greatly so its magma oozes up slowly through the vent which is the opening or the mouth of the volcano The magma stays around the vent since it is very thick and sticky This causes it to stay around the vent and cool off there As more persistent magma rises it pushes the cooled lava and asserts itself around the layer This consists mainly of an expansion from within the dome It can either result from a single eruption or a series of many eruptions
They can grow to their fullest from as little as a few days to as much as a century Usually the dome acts like a cork and cools down blocking the vent But another situation can exist where the lava cools down on top of the vent it may crack due to the further magma oozing out of the hard cooled down lava layer Those cracks breaks apart and causes debris spilling loose fragments along the flanks of a volcano At its worst case scenario the dome will grow out of its size and collapse This will cause something similar to a tsunami and a massive landslide combined As it collapses it brings along an ash cloud surge causing a deadly pyroclastic flow Pyroclastic flows are composed of fast moving shattered lava fragments volcanic ash and air rushing down the flanks of a volcano It's hot expanding gases causes a sightful scenery and resembles a snow avalanche It is fiery toxic gases that move at hurricane force speeds at a rate of over 100 kilometers per hour An eruption column and an eruption cloud can form when the gas and volcanic ash mix An eruption column is a cloud of gases and toxic ash that suspend in air after the pyroclastic flow It cools in the air and becomes too cool If the gas and ash ratio is high then a pyroclastic surge will occur which are so strong that they can go up hills and across streams The temperature of the air around the surge is about 300 degrees Celsius or 570 degrees Fahrenheit and the actual surge can exceed 1000 degrees Celsius This can destroy anything within its path in a matter of seconds With the steep sides of lava domes it can also cause rockslides This can bury the landscape and cause forest fires if the lava is still hot Pyroclastic flows and surges can explode at any time with no warning and have killed thousands of people in the process
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