A Convergence of Wonders is a chronicle of our recent journey through the Pacific Northwest and Northern Rocky Mountains. This the second day's story...
Our day was going to be spent on the two largest volcanoes of the Cascades, and hardly anyone has heard of either of them: Medicine Lake Highland, and Newberry Caldera. Crater Lake was slated to be on the day's menu, but 10-12 feet of snow still coated the rim, and we just weren't going to see it this time around. Both Medicine Lake and Newberry have been called basaltic shield volcanoes, but they are more complicated than "normal" shields with a variety of lava and magma compositions and are described as "shield-shaped volcanoes". We started the day on the flank of Medicine Lake Highland, but we couldn't actually see the volcano until mid-day, when we were far enough away. It is the largest single volcano in the Cascades with a volume of around 130 cubic miles (Shasta has around 85-100 cubic miles).
The best known part of Medicine Lake Highland is Lava Beds National Monument, where we spent the night. The park preserves a series of basalt flows that developed a network of lava tubes, underground conduits that allowed the basaltic lavas to flow for miles before cooling. The tubes drained at the end of the eruption, leaving a series of caves. Lava Beds preserves the largest concentration of lava tubes in North America, in excess of 700, with a combined length of more than 30 miles.
The students had explored a few of the lava tubes the previous night, so we sampled just two in the morning. Valentine Cave is in a separate younger flow, and is remarkably clear of debris and easy to walk through (the CCC cleared much of the talus in the 1930s). It has most of the interesting cave features such as lavacicles, bathtub rings (lava benches), rafted boulders, lava falls, and pahoehoe flows on the cave floor.
Skull has the largest opening of any cave in the park because it is part of the main feeder tube that transported the lava for 10-15 miles. Unlike the smaller caves, the main tube is relatively unstable, and huge blocks of basalt have broken off the ceiling and littered the cave floor to the extent that few original flow features are visible. It was so large I half-expected to see Han Solo, the Millenium Falcon, and a giant space worm in there.
detailed commentary on the battles that took place in my Other California series about Lava Beds. In short, the Modocs held the advantage of knowing the territory, and of taking shelter at Captain Jack's Stronghold, a natural fortress that was almost impossible to take as long as there were a few armed defenders. Pressure ridges and schollendomes provided the trenchs and "castle" walls that made the stronghold practically impregnable.
more info on the panel here.