Why are the largest volcanoes on Earth so much smaller than the ...

[itsmyluck]

Why are the largest volcanoes on Earth so much smaller than the largest ones on Mars?
 
  What will be an ideal response?

Question 2

What evidence suggests that Mars had an active hydrologic cycle in the past?
 
  What will be an ideal response?

[wuly]

Answer to Question 1

Plate tectonic processes on Earth keep things moving around, so a mantle plume creates a volcanic chain such as the Hawaiian Islands. Plate tectonics on Mars is absent, however, so successive eruptions accumulate in the same location, creating very large volcanic structures.

Answer to Question 2

Mars has all kinds of stream-like features carved into its surface, which most likely are the result of the work of running water.

[itsmyluck]

Excellent

[bdobbins]

Thanks for the timely response, appreciate it