To increase the amount of virtual memory go to Control Panel > System > Advanced > Performance > Settings > Advanced > Virtual Memory Change > Custom Size > adjust as needed. 2 times your physical RAM is a good minimum and 3 times your physical memory in MB is good for your maximum.
The three different types of lava differ in composition and flow rate. Rhyolitic lava is the slowest moving type of lava, since it has a high viscosity due to a high silica concentration. Basaltic lava is the fastest moving lava because of its low viscosity resulting from a low silica content.
They hope the lava will stay in the channels and not flow over the houses. There are a lot of factors that cause lava to be different - temperature, chemical composition, and amount of pressure all contribute to different types of volcanic flows. Just by looking at the lava thousands of years after the eruption, you can see exactly what type of flow it was.