Volcanic necks, also called volcanic plugs, are the remaining pieces of an old volcano. It is made when a volcano dies. The last remains of lava inside the volcanoes opening cool and harden. The neck was what once was the volcano’s opening. Over hundreds of thousands of years, erosion removes the rock around the neck. This leaves only the harder neck behind.
When a volcanic neck is forming, it can cause a large build up of pressure if the magma is trapped underneath it. If this occurs, an explosive eruption can occur. But, if this does not happen then erosion removes the surrounding rock. The neck then remains to form a distinctive landform.
Examples of Volcanic Necks
Volcanic necks are found all over the world. You have probably seen a volcanic neck and didn’t even realize it! In Yosemite National Park, the landform known as Little Devils Postpile, is actually a volcanic neck.
It is usually pretty easy to spot a volcanic neck. However, sometimes they can be difficult to spot if erosion has gotten to it. Volcanic necks typically stand up tall from the surrounding ground. They will typically have a very jagged structure and sometimes be pointed near the top. However, if erosion has worn the volcanic neck down, they will look more like very large hill.
North Berwick Law
An example of this would be North Berwick Law. The neck of this once standing volcano is made of phonolitic trachyte, which is a type of igneous rock. Unfortunately, due to erosion, the volcanic neck can no longer be seen.
For more information on volcanic necks, watch this great video:
Other Useful Resources:
More on Volcanic Necks: http://www.landforms.eu/Lothian/volcanic%20neck.htm
Facts about Volcanic Plugs: https://kids.kiddle.co/Volcanic_plug
What is a Volcanic Neck?: https://www.universetoday.com/39717/volcanic-neck/