Abstract
Deltas are important landforms on Mars because they indicate past
fluvial activity, contain a sedimentary record amenable to study, and
have the potential to store past signs of life. The sedimentary records
that are visible today on satellite and rover images are used to deduce
the fluvial and climate history of Mars. To do this we use our
understanding of deltas on Earth, as deltas are well-studied landforms.
However, when making interpretations it is very important to understand
the differences in delta morphodynamics and stratigraphy between Earth
and Mars. Even though the processes on Mars are similar, the water
discharge, sediment flux, and grain size sorting can be significantly
different due to for example gravity, sediment density, presence of ice,
and lack of ecology. In this research, we focus on the effect of gravity
and its net effect on delta morphology and stratigraphy. From
preliminary experiments, we expect a significant effect of gravity on
grain size sorting, because suspended sediment (fine grains) is affected
more by gravity than bedload transport (bigger grains). In addition, we
expect bigger grains to travel in suspension on Mars under the same
boundary conditions. We will study the net effect of these water and
sediment fluxes on morphology and stratigraphy by numerical modelling in
Delft3D. This software is typically used for river and coastal systems
on Earth, but we adapted the software by identifying all explicit and
implicit dependencies on gravity, so it can also be used for deltas on
Mars. We developed a 2DH hydro-morphodynamic model of a simplified delta
to test different scenarios. The model consists of a straight channel
flowing into a sloping basin. In the comparison between our Earth and
Mars scenarios, gravity is the only parameter varied. We are currently
experimenting with different upstream boundary conditions that we keep
equal between the Earth and Mars scenario. We are testing equal
discharge, water level, and sediment input. Equal discharge reveals the
effect of gravity on sediment flux, equal water level the effect on
water and net sediment flux, and equal sediment supply focusses on the
sediment sorting that is mostly overshadowed in the other scenarios by
the sediment flux difference.