detecting sharp bursts in several variables simultaneously in R

Question

i try be clearly. here data

dt=structure(list(x1 = c(28.5, 25.5, 28, 27, 29), x2 = c(28.5, 25.5, 
25, 25.5, 29), x3 = c(8, 5.5, 8.5, 7.5, 8), x4 = c(8.5, 6.5, 
6.