Hi All. Most of you are probably already aware of the growing volcano (400,000 years from now) at Lake Pillsbury in Northern California. A couple of years ago Petra and I took a tour there and talked to the locals. There were a lot of earthquakes occurring in the area and we wanted to know if there was anything the locals were aware of.

The first thing we learned is that the road leading to the area isn’t for the faint hearted. It isn’t paved for most of the way. As a matter of fact you can buy “T” shirts at the little general store there acclaiming the fact that you survived the road to Lake Pillsbury.

The locals told us that they have felt some of the quakes in the area, but more importantly they have smelled the odor of sulphur from time to time and that there are some hot springs on the east side of a range of mountains north of Lake Pillsbury. No hot springs in, or near the Lake Pillsbury area.

As the triple junction system moves north, it makes a hole in the mantle, which fills with a partially molten mantle rock including basaltic elements. One of the consequences of the plate geometry in the area is that south of this triple junction region, the base of North America is exposed to the deeper levels of the mantle. There is no intervening shield of partially solidified mantle so this hot rock comes straight up, reaches the base of the crust, and in the process undergoes a phenomenon called decompression melting, producing some volume of basalt, an intermediate rock. This process goes on as this region moves upward and it has left behind a string of volcanoes, all but one of which are extinct. The Clear Lake area, just 50 miles south of Lake Pillsbury, is the last active site with modern geothermal activity and is now used as hot springs and a spa. This is also the area where geothermal electricity is being produced.

The study covered a 90-square-mile area, and the researchers have seen evidence of magma everywhere under that patch. Interlaced basalt is intruded into about 10 percent of the lower crustal layer, a layer 3-4 miles thick. The researchers' results show that the magma is about 12 miles into the crust.

"The prognosis," Levander said, "depends upon global plate movement. If the plates choose one direction to move in, they could shut the system off. If they choose another they could accelerate it and if they continue with the current one, my guess would be that it might produce a Clear Lake-type volcanic field."

Says Henstock, a senior research fellow at Rice, "There are some reasons why Lake Pillsbury could be a good place for it to happen, but it could equally skip Lake Pillsbury and not show up at the surface until another 31 miles north, where there's another region that's a candidate."

Now for the reason for my posting of this little trivial information. I have been aware of the “slab window” or “slab gap” as some call it for sometime now, but have never really dug into it until just recently. Here is a link to the “slab gap” data. I’ll let you draw your own conclusions. Take Care…Don in creepy town

• Slab Gap