How violent the eruption is depends on the amount of silica present in the magma. Silica produces a thicker magma that is better at trapping gasses. The more gas present the greater the pressure. Therefore the more silica present in the magma the more violent the eruption will be.
Types of lava and their effect on the volcano structure There are two types of lava, acidic and basic. Acidic lava has a high silica content and this makes it thicker. Combined these cause the volcano to have a steep sided cone. These are known as Cone Volcanoes. Basic lava contains less silica, this allows the gasses to escape and gives a runny lava.
Eruptions of this type of lava a gentler and this along with it being runny allows the lava to flow further. Volcanoes of this type of lava will have gently sloping sides. They are known as Shield volcanoes. For more information on the types and shapes of volcanoes see Tulane University website How can we forecast volcanic activity?
By studying the type of materials and distribution of deposits geologists can learn a lot about the activity of volcanoes. Eruptions can be predicted in a number of ways: Tiltmeters are very sensitive devices that are used to identify any bulging of the sides of a volcano. Gases or steam coming out of vents in the volcano or the appearance of geysers could suggest an eruption will soon follow.
Seismometers are used to detect vibrations in the rock. These could be caused by the movement of the magma or the cracking of rocks due to increased hea both of these would indicate an eruption being imminent.
For real time monitinrg of the worlds volcanoes see the World Organisation of Volcanic Observatories website Ireland and Volcanoes Ireland is not known for its high level volcanic activity in recent history but by studying the landscape volcanoes from hundreds of millions of years ago can be still be seen.
These volcanoes are all extinct with the last eruption was approximately 60 million years ago. Today the Geological Survey continues to identify previously undiscovered volcanoes hidden beneath the surface of Ireland.
To learn more about these Geophysical surveys visit the Tellus page. The Smithsonian Global Volcanism Program defines a volcano as active only if it has erupted in the last 10, years. Another means for determining if a volcano is active comes from the International Association of Volcanology, who use historical time as a reference i. By this definition, those volcanoes that have erupted in the course of human history which includes more than volcanoes are defined as active.
However, this too is problematic, since this varies from region to region — with some areas cataloging volcanoes for thousands of years, while others only have records for the past few centuries.
As such, an "active volcano" can be best described as one that's currently in a state of regular eruptions. Maybe it's going off right now, or had an event in the last few decades, or geologists expect it to erupt again very soon. In short, if its spewing fire or likely to again in the near future, then it's active! Meanwhile, a dormant volcano is used to refer to those that are capable of erupting, and will probably erupt again in the future, but hasn't had an eruption for a very long time.
Here too, definitions become complicated since it is difficult to distinguish between a volcano that is simply not active at present, and one that will remain inactive. Volcanoes are often considered to be extinct if there are no written records of its activity.
Nevertheless, volcanoes may remain dormant for a long period of time. For instance, the volcanoes of Yellowstone, Toba, and Vesuvius were all thought to be extinct before their historic and devastating eruptions. The same is true of the Fourpeaked Mountain eruption in Alaska in Prior to this, the volcano was thought to be extinct since it had not erupted for over 10, years.
And so a dormant volcano is actually part of the active volcano classification, it's just that it's not currently erupting. Geologists also employ the category of extinct volcano to refer to volcanoes that have become cut off from their magma supply. There are many examples of extinct volcanoes around the world, many of which are found in the Hawaiian-Emperor Seamount Chain in the Pacific Ocean, or stand individually in some areas. For example, the Shiprock volcano, which stands in Navajo Nation territory in New Mexico, is an example of a solitary extinct volcano.
Edinburgh Castle, located just outside the capitol of Edinburgh, Scotland, is famously located atop an extinct volcano. But of course, determining if a volcano is truly extinct is often difficult, since some volcanoes can have eruptive lifespans that measure into the millions of years. As such, some volcanologists refer to extinct volcanoes as inactive, and some volcanoes once thought to be extinct are now referred to as dormant.
In short, knowing if a volcano is active, dormant, or extinct is complicated and all comes down to timing. And when it comes to geological features , timing is quite difficult for us mere mortals.
Individuals and generations have limited life spans, nations rise and fall, and even entire civilization sometimes bite the dust. But volcanic formations? They can endure for millions of years! Knowing if there still life in them requires hard work, good record-keeping, and above all immense patience. Explore further. More from Earth Sciences. Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page.
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When this material escapes, it causes an eruption. An eruption can be explosive, sending material high into the sky. Or it can be calmer, with gentle flows of material. This photograph shows an eruption of Mount St. Helens in Washington in July This eruption sent ash 6 to 11 miles kilometers into the air, and was visible in Seattle, Washington, miles kilometers to the north.
These volcanic areas usually form mountains built from the many layers of rock, ash or other material that collect around them. Volcanoes can be active, dormant, or extinct. Active volcanoes are volcanoes that have had recent eruptions or are expected to have eruptions in the near future. Dormant volcanoes no longer produce eruptions, but might again sometime in the future. Extinct volcanoes will likely never erupt again. Volcanoes occur when material significantly warmer than its surroundings is erupted onto the surface of a planet or moon from its interior.
Volcanoes on Earth form from rising magma. Magma rises in three different ways.
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