Hi M.J, Canie. Thank you for the complement Canie. Expert I’m not. I just know how to find the information and answers to questions.

M.J. asked a question about harmonic tremors so from that I gather it is volcanos that the question is about. Caine has provided some very good sites regarding volcanic tremors.

Volcanic seismicity has three major forms: short-period earthquakes, long-period earthquakes, and harmonic tremor.

Short-period earthquakes are like normal fault-related earthquakes. They are related to the fracturing of brittle rock as the magma forces its way upward. These short-period earthquakes signify the growth of a magma body near the surface.

Long-period earthquakes are believed to indicate increased gas pressure in a volcano's "plumbing system." They are similar to the clanging sometimes heard in your home's plumbing system.

Harmonic tremor occurs when there is sustained movement of magma below the surface.

Patterns of seismicity are complex and often difficult to interpret. However, increasing activity is very worrisome, especially if long-period events become dominant and episodes of harmonic tremor appear.

Ground Deformation

Swelling of the volcano signals that magma has accumulated near the surface. Scientists monitoring an active volcano will often measure the tilt of the slope and track changes in the rate of swelling. An increased rate of swelling--especially if accompanied by an increase in sulfur dioxide emissions and harmonic tremors--is a sure sign of an impending event.

Long Valley Caldera is a good example of a new volcanic eruption in the making. Of course that eruption may never take place in our lifetime, or even a couple of our lifetimes. Take Care…Don in creepy town.

• Long Valley Caldera