This canyon was not created by the erosion of water, like the Grand Canyon, but by tectonic motions that fractured the crust. On Earth, the biggest volcano is Mauna Loa with a base of 120 km and rises nly 9 km above the ocean floor. Olympus Mons is so much taller and bigger than the volcanoes on Earth or on Venus because Mars is much smaller, and so the gravitational pull is weaker. There are hundreds of volcanoes on Mars, but none appear to be active. Craters Craters on Mars are more easily eroded than on the Moon or Mercury because of the dust storms.
Sand fills and erodes the craters rather efficiently.
The ejecta from craters, that is, the material expelled during the impact that formed the crater, have very different appearance on Mars and on the Moon. On the Moon, the ejecta appear dry. Slide of Moon ejecta On the martian craters, the ejecta appear to have been watery . It is ironic that a closer look at Mars actually did reveal channels that once appear to have carried water. But these channels do not look straight and designed by intelligent life.