NOVA Rockies 2009
WHAT ARE THE RINGING ROCKS?
The Ringing Rocks are a small portion of the region known as the Boulder Batholith. The Boulder Batholith is Cretaceous in age and composes the mountain ranges between Butte and Helena. The Ringing Rocks themselves are an exposed igneous pluton which has been exposed at the surface due to a downdrop of the land surrounding it. The pluton has since curmbled apon itself giving its appearance today as a strange pile of boulders. The way the pluton fell to pieces is unique. The ringing rocks are all boulders. You can find no gravel or smaller sized particles in the pile. The Rocks are mafic and coarse-grained, and we interpret them to be gabbro. The boulders are very angular in shape making them unique from the surrounding granitic plutons. The rocks themselves weather a rust red on the surface due to iron oxide and are pitch black on fresh surfaces. The truly remarkable thing about these rocks, is that when they are struck with a hammer or rock, they create banging or ringing noises of various volumes and pitches.
WHERE ARE THE ROCKS THAT RING?
The Ringing rocks are located just north of interstate 90 about 20 miles east of Butte. In the above photo you can see the large Boulder Batholith with the cross-hairs on Ringing Rocks. Below is an enlarged photo of the area in the cross hairs.
You can now clearly see the red color of the pluton known as "Ringing Rocks" slightly northwest of the cross-hairs. Notice that nothing in the imediate surrounding area shares the same color or form as this pile. Ringing Rocks is one in a million.
The Theories behind the ring.
The truth is nobody actually knows exactly why the rocks that compose this pluton create this spectacular ringing noise. Many people have drawn theories to why and how they ring and the basis of my study is to speculate a theory as well.
The rocks make a ringing noise similiar to a bell. Some believe that there is metallic material inside of the rocks creating the noise. Another theory is that it has to do with the way the rocks are positioned on the pile, this theory is supported by the observation that the rock no longer seems to ring once it is taken off of the pile.
The theory that I support is that the ringing is a combonation of the position of the rock, the rocks composition and the effect of resonance within the rock, and surrounding rocks.
First I will begin by listing the observations from my personal visit to the ringing rocks.
1.The rocks are all boulder in size.
2.They ring when you hit them with rocks,hammers, wood.
3.Larger boulders seem to make higher pitched rings than smaller boulders.
4.Thinner protuberances of rock seem to make particularly loud rings as compared to solid large boulders.
5. The rock makes no audible ringing when taken from the site.One rock that I hammered on had a u shaped recess in it. On the left side of the recess is the main chunk of the boulder, on the right side, the boulder is only about 3 inches thick, the recess was a bout 12 inches deep. when you banged on the large piece of the boulder on the left side of the recess, it made a high pitched low volume "ting" when you hammered on the thin section of rock composing the right wall of the recess it created a loud "bang" that could hurt the ears.
7. When a hand was placed at point x and the rock was struck near point x the hand would feel no vibration. When a hand was placed a point x and the rock was struck from point y the hand felt considerable vibration.
One of the first connections I made was between the rocks at Ringing Rocks, and bells. The reason a bell makes the noise it makes is because of the physical composition of the bell, the thickness of the material used to make the bell, and the shape of the bell. The noise that is produced from a bell is a result of the resonance it creates, sound waves bouncing around in the hollow recess of a bell hold the tone for a bell and can amplify the sound. I believe this is the same reason we are able to hear sound at Ringing Rocks. Certain studies have shown that the rocks do emit sound when separated from the pile. However the sound emitted is not loud enough for the human ear to hear. Which suggests that the placement of the rocks seem to amplify the sound created by the resonance from within these rocks, similar to the way sound waves bounce around inside a bell, sound waves bounce between these rocks. Another connection I made was from observation 6 and 7. The rock was much louder and clearer when struck at point "Y." Vibrations could be felt in the rock as well when the
rock was struck here. I believe the resonance created by the u shaped recess and the freedom of movement the thin piece has, can create a more violent resonance than a large solid piece. This creates a louder ringing for us to hear.
The composition and texture of the rock has to play a significant role in the creating of sound. Perhaps the crystalline structure of the gabbro has the ability to create these sounds by the spacing of crystals and
the connections between them. This can be strongly affected by the rate the magma in the pluton cooled. An extension of this idea is that the Ringing Rocks pluton might have cooled under conditions that are unique among all other plutons, allowing the crystalline structure to form the way it did, and allowing the rocks to create their distinct sound.
Another Ringing Rocks?
There is another location in the United States with rocks that ring. It is in eastern Pennsylvania. Several locations that have ringing rocks are reported in that immediate vicinity. I hope to travel there and add my observations to this part of my report.
notes, personal observations