The yarn number is the length in yards of one pound of the yarn, divided by 1600. Symbol Nar. This is the same as the weight in ounces of 100 yards. So one pound of number 1 run yarn is 1600 yards long, one pound of number 2 run yarn is 3200 yards long, and so on.
As with most other volcanoes in the Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava rock interlayered with ash, pumice, and other deposits. The mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted.
Geologists call Mount St. Helens a composite volcano (or stratovolcano), a term for steepsided, often symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris. Composite volcanoes tend to erupt explosively and pose considerable danger to nearby life and property.