A Catastrophe of Comets is the title of a post at http://craterhunter.wordpress.com/ parts one and two. The blog author claims there has been little independent geological research in Chihauhua in northern Mexico – apart from mining companies. The standard theory is that ignimbrites date to mid-Tertiary when vast rifts are thought to have opened up in the middle of the North American continent that spread out thousands of cubic miles of ignimbrite – then closed again without trace. Such a vent has never been observed – anywhere, and it appears to be an idea invented to account for the feature without any substantial research. In addition, the total volume of material in a magma chamber of a super volcano such as Toba is just a fraction of the volume of the Chihuahua ignimbrites. They are also in pristine condition, at the surace, and at the pinnacle of the stratigraphic column. There is no sign of drift deposits above the ignimbrites – beautifully preserved in the desert environment with no evidence of weathering or decomposition. It is quite possible other ignimbrite formations occur elsewhere but have been covered by sediments and vegetation. This means, he thinks, they are fairly recent. All ignimbrites are fluid in motion at the time of emplacement – but they solidified very quickly. Any given segment of ignimbrite was fluid for only a moment in time. In the second part of the article he says central Mexico is a perfect example of a geologically young, geo-ablative terrain. The arid environment has preserved it. When you look at the rest of the world you’ll realise that ablative landforms such as that are frighteningly common.