Choice of Words: Mountains are like people reaching up, and sky is like a ceiling. So mountains touching the sky is like people reaching up to touch a ceiling.
Alternative Expressions
The mountains were so tall that they seemed to touch the sky.
Meaning: This means that the mountains were so tall that they looked like they were touching the sky.
Choice of Words:Mountains are tall, rocky landforms that rise above the ground. So is used to emphasize how tall the mountains were. Tall means having a great height. That introduces a dependent clause. Seemed means to appear or give the impression of being something. Touch means to make contact with something. Sky is the space above the Earth where the sun, moon, and stars are. When you put them together, "The mountains were so tall that they seemed to touch the sky" is a more detailed way of saying that the mountains were very tall.
The mountains pierced the heavens.
Meaning: This means that the mountains were so tall that they seemed to reach up into the sky.
Choice of Words:Mountains are tall, rocky landforms that rise above the ground. Pierced means to make a hole in something. Heavens is a poetic way of referring to the sky. When you put them together, "The mountains pierced the heavens" is a dramatic way of saying that the mountains were very tall.