Version 2.8 of Underworld has been released recently. As with all major releases, this release brings numerous new features, enhancements and bug fixes. A summary of changes may be found within the usual CHANGES.md file. As is also usually the case, numerous API changes have been necessary or warranted.

Viscoelastic materials exhibit the properies of both solids and liquids, with deformation rates dependent on both the viscous stress and elastic stress rate.

(they don't make them like they used to ... ) Cratons are anomalously-strong regions of the continents that have largely resisted tectonic forces for billions of years. How such strong zones could be forged in a hot, low-viscosity, low stress,  early-Earth has been a long-standing puzzle for geologists.

Modelling the relative time-scales of the Rayleigh-Taylor Instability and delamination, using Underworld With Adam Beall, Cardiff University. Why model sub-continental gravitational instabilities? Within the plate tectonics framework, continents are generally considered to have a much lower density than the asthenosphere below and therefore avoid the kind of recycling that the oceanic crust and lithosphere undergoes.

Using physical units and how to appropriately scale a model is a top question users ask when beginning with Underworld. The equations Underworld solves are stated in a physically correct form, they remain valid as long as every material constant, geometry, time, etc., are expressed in the same system.  There is no explicit concept of units no scaling in Underworld, the choice is entirely left to the user.

In honour of Hans Mühlhaus' 70th birthday this month, here are some shear band simulations made with Underworld. We are investigating the role of dilatancy in the geometry of the shear bands for a box of material when a small trapdoor is opened. The extent to which large-scale deformation is needed to release material through the trapdoor depends on how much the material dilates when shear bands form.

Underworld2 is a python-friendly version of the Underworld geodynamics code which provides a programmable and flexible front end to all the functionality of the code running in a parallel HPC environment. This gives signficant advantages to the user, with access to the power of python libraries for setup of complex problems, analysis at runtime, problem steering, and coupling of multiple problems.

(aka the Underworld renovation project) Underworld is our parallel, particle-in-cell, finite element geodynamics code [1]. For the past year or so, the Underworld team has been working on a refurbished user interface. We've known for a long time that it needed to be done but we finally bit the bullet.

In a recent paper [1], we used Underworld models to examine subduction congestion associated with the ingestion of a continental ribbon. The SE Australian geological record turned out to be a wonderful place to study this process. Here is a short summary of the work for a relatively non-technical audience that we put together and some additional figures which I prepared.