Which of the following is true concerning the 1980 eruption of Mt.St.Helens?
A)The eruption was a complete surprise to geologists and provided no forewarning.
B)The eruption produced the largest basalt flow of the 20th century anywhere on Earth.
C)The eruption began with a lateral blast of debris that was ejected at the speed of sound.
D)No lahars were produced because the eruption occurred in the winter.

Question

Quizplus · Accepted Answer

The Mt. St. Helens eruption in 1980 began with a lateral blast of debris that was ejected at the speed of sound, which is estimated to have been equivalent to 24 megatons of thermal energy. This lateral blast caused widespread destruction and was the most powerful explosive event of the eruption.

Answer: D
 This statement is false. The Mt. St. Helens eruption in 1980 did produce significant lahars (mass flows of volcanic debris mixed with water) that caused extensive damage to surrounding areas. The fact that the eruption occurred in the winter may have contributed to the lahars by increasing the amount of meltwater from snow and ice.

Which of the Following Is True Concerning the 1980 Eruption