Some craters in the Amenthes region show ejecta around them that have lobes. It is believed that the lobed shape is caused by an impact into water or ice logged ground. Calculations suggest that ice is stable beneath the Martian surface. At the equator the stable layer of ice might lie under as much as 1 kilometer of material, but at higher latitudes the ice may be just a few centimeters below the surface. This was proven when the landing rockets on the Phoenix lander blew away surface dust to reveal an ice surface. The larger an impact crater, the deeper its penetration, a large crater is more likely to have a lobate ejecta since it went down to the ice layer. When even small craters have lobes, the ice level is close to the surface. This idea would be very important for future colonists on Mars who would like to live near a source of water. Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. Sometimes craters will display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters can show us what lies deep under the surface. One crater in the Amenthes quadrangle is believed to be a source of nakhlitemeteorites. A team of researchers found that these particular meteorites came from four different eruptions of lava because they showed different ages. The ages were measured by comparing isotopes of the element Argon. Since the ages vary from 93 to 1322 million years, the authors concluded that volcanoes grow much more slowly on Mars than the Earth. Many of the volcanoes on the Earth grow much quicker, as they form at plate boundaries. In contrast, Martian volcanoes probably form from plumes.
Hebrus Vales has tributaries, terraces, and teardrop shaped islands. The tear drop shape of the islands indicate what direction the water used to flow. The terraces may be caused by different layers of rocks or from the water being at different levels. These features are common for the rivers of the Earth.
Streamlined shapes
Streamlined shapes are formed from erosion by flowing water.
Cones
Mesas
Mesas form when erosion has removed much of the surrounding ground. They are the remains of material that once covered a wide area.
Fossae
The Amenthes quadrangle is also home to troughs called fossae in the geographical language used for Mars. These troughs form when the crust is stretched until it breaks. The stretching can be due to the large weight of a nearby volcano.
