Faulting, Volcanism, and Life in Northernmost California: the Tulelake Graben

Gillem's Bluff at Lava Beds National Monument

Lava Beds National Monument at the extreme north end of California is a fascinating place. It preserves hundreds of lava tubes and lava flows only a few thousand years old. It also preserves the memory of a people, the Modoc tribe, who were destroyed so settlers could raise alfalfa and potatoes. And there are lakes that formerly gave life to millions upon millions of birds. The smaller lake that persists (with human help) provides shelter for the migratory birds who remain. The lake basin below Lava Beds is protected as the Tulelake National Wildlife Refuge.

Multiple fault scarps (the shadowed terraces) cross the region north of Lava Beds National Monument

It began with faulting. The crust in this region has been stretched beyond the breaking point, and some of the fault blocks have sunk against the others, forming a series of horsts (the uplifted blocks), and one deep graben (the sunken block). The main fault scarp in the top picture is called Gillem's Bluff. One can just make out the waters of Tulelake at its base.

The faults provided an avenue for basaltic magma to reach the surface. The rough blocky a'a lava in these photographs is the Devil's Homestead flow, which emerged just over 10,000 years ago from fissures at the Fleener Chimneys in Lava Beds National Monument.

The graben became a collecting sump for waters in the Klamath River drainage. The present incarnation of Tulelake covers only about 15 square miles (five miles long and three miles wide), but the lake once extended across one hundred square miles. Diversions of the rivers that fed the lake caused vast portions of the lake to dry up and the new land was converted to agricultural fields. Not that the original European settlers particularly cared, but the lake was a critical stop where migratory birds rested and fed during their long journey between the Arctic regions and their winter homes in central and southern California. The topography literally funneled the birds through to Tulelake and  the Klamath Lakes a bit farther north. The lands here are mostly arid, and the water was a sanctuary.

The birds still come, Sandhill Cranes, Ross's and Snow Geese, Greater White-fronted Geese and many others, more than a million each year, but they face challenging conditions of overcrowding and disease, especially in dry years when there is less water and food (the lake is at the end of the receiving line in terms of water allotments). Avian cholera sometimes kills thousands of them. But they've survived, and I hope they will continue to do so.

Earthly violence in the form of earthquakes and volcanic eruptions created this strange landscape, but water made it productive and full of life. It's a fascinating place to visit, especially in spring and fall when the bird migrations peak.

The Other California: Fleener Chimneys, Spatter Cones and Fault Scarps

This post continues our exploration of one of California's hidden corners, Lava Beds National Monument, on the flank of California's biggest volcano, the Medicine Lake Highland.

So what, pray tell, is the feature below? A Sarlaac from a Star Wars movie? A Doomsday Machine from Star Trek? Brendan Fraser's pathway to the center of the earth? No, it's one of the abandoned volcanic vents from Lava Beds, the Fleener Chimneys. There are three holes like this, around fifty feet deep, that were the conduits for the Devil's Homestead Lava Flow around 12,000 years ago.

The eruptions were mildly explosive and messy, at least in the final stages. The Fleener Chimneys (below) are spatter cones, formed as molten bits of basalt were flung from the vents. Lava emerged and almost immediately floweed into lava tube systems, the openings of which can be seen in the near vicinity. After traveling some distance, the lava flows cooled enough to start forming a'a flows that give the Devil's Homestead its characteristic appearance.

Another fine example of a spatter cone, much younger and fresher looking, can be seen at Black Crater, just a short distance away from the Fleener Chimneys turnoff on the main park road. It erupted only about 1,250 years ago, but might as well have been yesterday given its youthful appearance.

Why have these eruptions occurred on the lower flanks of the Medicine Lake Highland? A stereotypical volcano has a crater at the summit that produces the explosions, the ash, and the lava flows. As has been pointed out previously, the Highland is a unique exception to the "rules" of volcano types. Shaped like a massive shield, it has numerous small magma chambers with a variety of magma compositions. Fluid basalts follow weaknesses in the crust, and fault zones make a fine conduit to reach the surface.

Medicine Lake Highland sits at the boundary between the Cascades and the Modoc Plateau, and fault zones project into the volcanic edifice. Gillems Bluff, seen in the picture below, is a fault scarp, with the sunken graben of Tule Lake on the right side of the photo. It just happens that the fault that formed Gillems Bluff projects right through the Fleener Chimneys.

These features are easy to access during a visit to the park. If you are tempted to toss a rock into the Fleener Chimneys to see how deep they are, please resist the urge. A clean up crew recently removed 35 tons of rock from just one of the holes.