Rock Composition and Types

Each type of rock found at Lava Beds is categorized geologically by the amount of silica present. Silica is a glassy mineral that crystalizes and affects the viscosity of a lava flow. Basalt contains the least amount of silica out of all of the rocks at Lava Beds. The silica content of basalt is around forty seven percent. Basalt makes up the largest group of rocks at Lava Beds with ninety percent of the rocks being in this category.

Basaltic lava beginning to harden on the outside.

The liquid characteristics of basalt include extreme heat, and fluidity which allow it to flow freely and rapidly over large areas. This is why so much of Lava Beds is covered in lava tube caves and lava fields. Basaltic lava is categorized in two ways: Aa, and Pahoehoe. Aa is a term used to describe very rough and jagged basaltic rock. At Lava Beds this type of basalt can be seen at the Devils Homestead lava flow. Pahoehoe on the other hand is used to describe smooth and ropy basaltic rock. This is the type of basaltic lava that is perfect for forming lava tube caves.

The rest of the rocks at Lava Beds are primarily categorized as andesite. Andesite is a type of rock that contains significantly more silica than basalt. Andesite lava is thicker and more resistant to flow, which is the reason that this type of rock is primarily found in surface rocks surrounding Lava Beds.
 

Obsidian volcanic glass

Rhyolite is another type of rock found at Lava Beds. This rock has a silica content of 77 percent, making it extremely slow moving compared to basalt.
One type of rhyolite is obsidian, a volcanic glass that was one of the primary components of the Glass Mountain eruption around 900 years ago. Pumice is another type of rhyolitic rock that was also present in the Glass Mountain eruption. These two types of rhyolite are now present across the entire surface of Lava Beds.