Where on Mars are there other craters or collapse features with very high depth/diameter ratio?

Question

Figure 1 of this article about craters and collapse features on Mars with high depth/diameter ratios shows that ratios higher than 0.2 are exceptional.

This presentation of the Program of the Second MSL Landing Site Workshop about possible landing sites in Sinus Meridiani shows an image of a "crater" that is 2.4 km wide and 750 meters deep ! (But judging from the elevation chart of Mars Trek the crater is only about 100 m deep.)

Because the ratio of this feature is more than 0.3 and it has no clear rim, it is very likely that this is not an impact crater at all.

Unusually deep fresh craters were recorded in SW Utopia and Isidis Planitia in this article.

Are there more known features on Mars with such a very high depth/diameter ratio ?

Answer 1

The d/D ratio of Martian craters vary from 0.1 to 0.4 with mean value of 0.23. The largest crater with diameter 33m has d/D ratio of 0.2 but smaller craters have higher d/D value. One crater has a surprisingly high d/D value: 0.5. A plot of d/D ratio vs diameter is drawn showing the variation in the values:

Shallower craters have d/D values of less than 0.3

a: 0.50 ; b: 0.42 ; c: 0.39 ; d: 0.42

The variation in this value depends on target material properties like varying strength, porosity, or layering of targets; or impactor conditions such as impact velocity, impact angle, or physical state of the bolide (i.e., strength, fractured versus cohesive). The dependencies are listed below:

1. Spallation can be seen in targets with porosity up to 60%. The ratio of spall diameter to pit diameter is not strongly dependent on porosity and is between 1.5 and 3. The range of the ratio is similar to those found for microcraters on lunar rocks and glass targets in the laboratory.
2. The depth of a crater cavity is a function of the density ratio of the projectile and target. However, it is also dependent on the impact velocity and porosity of the target.
3. The normalized diameters of craters on porous targets tends to decrease with increasing target porosity. An empirical scaling law derived for porous sedimentary rocks based on conventional scaling laws is shown to be a reference for craters on brittle targets, including porous targets of various porosities.
4. The depth-to-diameter ratio of the crater cavity is roughly 0.5 for tuff and gypsum, with porosities of about 43% and 50%, respectively. On the other hand, the ratio is about 0.2 for sandstones and cement mortar, although the porosity of cement mortar is about 40% and similar to that of tuff. No strong velocity dependence is evident in the depth-to-diameter ratio, although the ratio changes with impact velocity for microcraters produced on non-porous glass.
5. Crater shape is roughly a trigonal pyramid for craters with a depth-to-diameter ratio of less than 0.3

References:

1. Daubar, I. J., C. Atwood-Stone, S. Byrne, A. S. McEwen, and P. S. Russell (2014), The morphology of small fresh craters on Mars and the Moon, J. Geophys. Res. Planets, 119, 2620–2639, doi:10.1002/2014JE004671.
2. Impact cratering on porous targets in the strength regime by Akiko M. Nakamura (PDF)

Answer 2

Credits: NASA/JPL-Caltech/University of Arizona

This image is a screenshot of the color version of HiRISE's ESP_043222_2035.
From Pit Crater near Elysium Mons:

This image was taken of an area on the lower southeastern flank of the volcano Elysium Mons. In the center is a small, dark pristine-appearing pit approximately 130 meters in diameter, which is clearly visible among the numerous small impact craters that are heavily covered by dust and sediment.

Garden variety craters are excavated by impacts and are characterized by raised rims, sloped walls and surrounded by ejecta blankets, but pit craters are simply sink holes in the ground with near vertical walls and floors that are only visible when the sun is high in the sky. They are deep holes that may lead to underground caves in volcanic terrain.

When the image was taken the Sun was about 51⁰ above the horizon, and we can see that the shadow of the crater rim then reached about the center of the floor.
So the depth of the crater floor center then is: tan 51⁰ x 65 m. = ~ 80 m., and the d/D ratio: ~ 0.6.