konstantin sivkov wrote that russia needs a new ` asymmetric ' weapon .
he says detonating nuclear weapons on seafloor would unleash tsunamis .
seismic activity would trigger volcano , pour feet of ash over the us .
he says tsunamis could affect 240 million americans and hit europe too .
analyst says new weapons could be ready within 10 years .
tv presenter previously said russia could turn us to ` radioactive dust '