Answer:
156.67 m/s
0.45676 times the speed of sound
Explanation:
Distance from the ground = 23.5 km = 23500 m
Time taken by the blast waves to reach the ground = 
Spedd of the wave would be

The velocity of the blast wave is 156.67 m/s
v = Velocity of sound = 343 m/s

The blast wave is 0.45676 times the speed of sound
Explanation:
Basaltic lava
Basaltic lava generally takes two distinct forms known by the Hawaiian terms pahoehoe and aa. Pahoehoe has a smooth wavy surface that resembles twisted rope. It advances by extruding molten toes of lava beneath a thin, flexible crust. As it travels pahoehoe lava often changes to blocky flows called aa.
The load is the weight of the rock that Jonathan lifts:

The effort instead is the force applied in input to the lever in order to lift the rock:

So, the ratio between load and effort for this exercise is

So, the ratio is 10:1.