# Question about melt transport in Melt Global Material Model

**URL:** https://community.geodynamics.org/t/question-about-melt-transport-in-melt-global-material-model/3602
**Category:** ASPECT
**Created:** [August 19, 2024, 4:15pm UTC](https://community.geodynamics.org/t/question-about-melt-transport-in-melt-global-material-model/3602 "2024-08-19T16:15:20Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![mmayle](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/mmayle/32/1556_2.png) [@mmayle](https://community.geodynamics.org/u/mmayle)
#### Post date: [August 19, 2024, 4:15pm UTC](https://community.geodynamics.org/t/question-about-melt-transport-in-melt-global-material-model/3602/1 "2024-08-19T16:15:20Z")

</div>

Hi All,

I noticed from the global melt parameter file (global\_melt.prm) the comment addressing the Reference bulk viscosity parameter:

```
# The bulk viscosity describes the resistance of the rock to dilation
# and compaction. Melt can only flow into a region that had no melt
# before if the matrix of the solid rock expands, so this parameter
# also limits how fast melt can flow upwards.
# The bulk viscosity is computed as the reference value given here times
# a term that scales with one over the porosity. This means that for zero
# porosity, the rock can not dilate/compact any more, which is the same
# behavior that we have for solid mantle convection.

```

The melt global material model is incompressible. Does this mean that melt global does not allow melt to migrate through material that has not melted before (where porosity = 0)?

Thanks!  
Micah