The quick hit devastation channel, which has high pressure, generates a cylindrical percussion wave. It is spread radial to the rod of the channel. The equation of the radial part of a strong cylindrical percussion wave is [69]:

r = S . ( W / d )^0,25 . t^0,5 ( 1 )

Here r-is the radius of air "cylinder", which has high pressure, s-is the collaborator erupting of the gas properties. For air it is equal to 1 approximately. W-is the energy separated on the each part of length (10⁵ r/m²), t-is time, d - is the density of environment.

Pressure, created by a percussion wave on the peak of a wave is calculated by the following formula:

P = 0,2 . w / r² ( 2 ).

As soon as P ~ 1/ r2, so strong pressure will become weak because of increase of radius, which will become a sound wave at last.

Let's estimate pressure values. From the center of devastation channel towards its ends. If r = 0,02 m, P » 500 atmosphere; r = 0,05 m, P » 80 atmosphere; r = 0,14 m.,

P » 10 atmosphere. For lower pressures the formula ( 2 ) is not applied.

Values of pressure, calculated by the formula ( 2 ), create the destructive factor of a lightning, which is considered to be the percussion wave ( Figure 64 ).

Figure 64. Dependence of percussion wave pressure on distance from the center of the devastation channel.

As it is seen from Figure 64, that part of a percussion wave has the main destructive power, pressure of which is bigger or equals to 500 atmosphere.

I observed the region of Tsak Kary caves, which are situated in the North of Armenia ( Lori region, Vardablur village ) with the goal to estimate the influence of a lightning percussion wave on caves. The observations showed, that a lightning percussion wave pulls up to 10 kg fragment of the basalt rock of a cave. It corresponds well to the results of people's hundred years observations, according to, which a lightning divides the mill stone, which has 20-30 sm. thickness [20].

It is easy to calculate the influence of a percussion wave on the caves, generated of other rocks, if we accept that influence opposite to degree of a comparative rock hardness. Hardness has the following values for different minerals: gypsum -2, sodium chloride -2,25, calcite -3, quartz -7 [70]. Hardness of basalt can be estimated as silicate hardness:5,5 - 6. There isn't hardness of limestone. There is hardness of calcite mineral generated of calcium carbonate -3. Limestone is harder than calcite, so we accept hardness equal to 4-5 for it.

The received values are presented in Figure 65.

Figure 65. Dependence of pulled off a cave rock volume, as the result of a lightning impact, on the degree of a rock, hardness.

It is possible to estimate the size of increase of a cave under the influence of a lightning impacts in 1 million years. It is necessary to have periodicity of a lighting devastation in a cave. Proceeding from the fact [20] of dry trees existence, often met near underground abysses, which became dry of a lightning impacts, periodicity of a lightning impacts is tens of years. Value of the same kind is presented in the ancient Armenian epic [20]:

David of Sasun will rise against you,

The sward Lightning will rise against you.

Let's accept frequency of a lightning impacts is one in a hundred years. In 1 million years quantity of impacts will be 10⁴ In different rocks, the volume of lightnigs influence will be during 1 million years: (Figure 66).

Figure 66. Dependence of pulled off different rocks fragments values ( D V ), as the result of a lightning impact, on time ( above - gibsum. NaCl, limeston, basalt ).

If there is a cave, which volume is 10³ m³ and its age is one million years, the size of influence on its formation will be: ( Figure 67 ).

Figure 67. Lightnings force size during one million years on the formation of the cave, which has 10³ m.³ volume.