What’s causing all the “boom” sounds lately in our area? My theory:

Since early this past weekend and into last night my Facebook, Twitter, and email have been filled with questions about loud “booms”. They seemed to be centered on Eastern Gaston County with a few in Stanly and Cabarrus counties. 

These were just from last night, but the reports go back well into the weekend.  I had reports from as far away as Stanly and Cabarrus Counties this weekend, but the most have been coming from eastern Gaston County. 

So what is going on?

I think I can break this down into to things.

  1. The cause which is still in question but I have some ideas.
  2. The reason so many people are hearing these and reporting them. This is actually weather related.

Possible Causes:

Not Earthquakes:

Sometimes these do make noise, but the great thing about earthquakes is we have sensors to measure them. There have been zero signs of Earthquake activity in the area. Either from the USGS or on any helicorder which records ground shaking. Even small quakes and even some large explosions should show up on a seismograph.

Sonic Booms: Possible but not likely.

While we certainly have lots of military aircraft in North Carolina and I wouldn’t rule this out. It does seem odd that this would be so close to the Charlotte-Douglas International and be happening so frequently. Though you just never know with the military they could be doing some kind of training that is no public. Though I doubt they would be doing is so close to Charlotte, and at the times and locations, the reports are coming from.

Explosions of some kind: Very likely.

Now, these don’t appear to be accidental explosions but possibly something more intentional. Over the years when we have had reports like this before. It has later been found that it was young adults or teenagers playing with Tannerite. What is Tannerite you ask? It’s a stable explosive often used in target shooting to make exploding targets. Primarily at gun ranges, often when enough is added in large quantities you can make a huge explosion by shooting it with a rifle, but not a fuse or electronic trigger.

Tannerite is the brand name of a patented[1] exploding target used for firearms practice, sold in kit form and containing the components of a binary explosive.[2] The explosive comprises a combination of ammonium nitrate and/or ammonium perchlorate (oxidizers), and a fuel – primarily aluminum powder – that is supplied as two separate powders that are mixed by the user. The combination is relatively stable when subjected to forces less severe than a high-velocity bullet impact, such as a hammer blow, being dropped, or impact from a low-velocity bullet or shotgun blast.[1] It is also not flammable – an explosion cannot be created by a burning fuse or electricity.[3] Because it is sold as two separate powders, it can be transported and sold in many places without the legal restrictions that would otherwise apply to explosives.[4] The target system as a whole is the patented, trademarked product called Tannerite, although the term is often used to refer to the explosive mixture itself, and other combination explosives are often generically referred to as Tannerite.[4]

So why so loud and heard by so many people?

This is where the weather plays a huge role. Since the weekend in the evenings and at night, we have had a pattern of temperature inversions. This is when cooler air is trapped near the surface, and warmer air is just up from the surface around 1-4,000 feet up. This is why we have had so much fog, low clouds, and drizzle lately as well.

INVERSION LAST NIGHT AROUND 8 PM

This inversion also has a side effect of causing atmospheric ducting. Atmosphere ducting can cause sound waves to travel very long distances. This happens when we get elevated thunderstorms; the thunder can sound really loud and also travel a great distance. The sound waves bounce back and forth between the ground and the inversion and travel instead of dissipating up. Think of a loud bang in a closed room versus outside in an open area. In this case, we don’t have thunder but explosions near the surface. So the sound is traveling far distances.

Conclusion:

I’m not entirely sure of the cause but highly suspect this is man made. Since we know, it’s not an earthquake, and no one has reported the explosion of property. I can only assume someone is setting off explosions either at a gun range with targets. Or that someone is just goofing around with tannerite out in the wood and not realizing how far the sound is traveling with the temperature inversions that have been in place the past few days.

If you hear anything or know anything please leave a comment in the section below.

 

 

  • robert gwiazdzinski

    It is more than sound, there is a significant, and i mean significant (house shaking) amount of vibration with it too.

    • wxbrad

      yes but the same atmospheric ducting of the sound waves would apply to shock waves. So large explosions would most certainly shake the house.

  • Debra Yarbrough

    I’m in Vale and I’ve been hearing them also. I even called the police about them! They didn’t know anything either.

  • jwpegram

    I would think Tannerite or a ground level explosion of such force to produce the sound wave people are hearing would register on siesmometers. What would be interesting to see is the decibel level at each report. A sonic boom would be fairly consistent I would think whereas something more explosive would dissipate over time and distance.

    • wxbrad

      unless you have an inversion to causes atmospheric ducting. Then no it would not dissipate normally.

  • DC

    Brad, as a fellow meteorolgist (not necessarily a practicing one in my job) I was curious about the atmospheric conditions and glad you posted the GSO Skewt from 00Z, about same time as the boom last night. I live in the zone and heard it distinctly. At that time there was an explosion nearby due to construction trash mixed with gasoline and ignition source. With this and the inversion my theory is that it carried the sound further than normal with the surface winds.

    • wxbrad

      Where was that explosion? Heard something about that exact thing last night to, but could not confirm.

      • DC

        I believe somewhere off Hickory Grove Road. This is also where a lot of folks were reporting the sound on Mount Holly Town Talk Facebook page.

        • wxbrad

          Thank you!

  • Big Education

    So why not thunder?