Geology Introduction to Lassen and Warner Valley Webcourse Click through the presentation before the fieldtrip to Warner Valley.

As you may know, the Earth can be categorized into three layers: the crust, mantle, and core. crust mantle core We live on the crust

The Earth’s crust is composed of tectonic plates that float on and move around relative to the underlying mantle. Press and Siever, 1998

Where plates collide, you have convergent boundaries Press and Siever, 1998

Where plates move apart, you have divergent boundaries Where plates move apart, you have divergent boundaries Press and Siever, 1998

At each of these margins you get volcanism! Press and Siever, 1998

You can also get volcanism in the middle of plates… like in Hawaii.. but that is a story for another day. Press and Siever, 1998

We are going to focus on the volcanism that occurs at a convergent margin where an oceanic plate is subducting beneath a continental plate. Press and Siever, 1998 Subducting means one plate is going underneath another, like right here

This type of volcanism is what formed the Cascade Mountain Range and the volcanoes at Lassen Volcanic National Park. Lassen is way down here!

Magma formation at subduction driven volcanoes looks something like this. modified from S. Rost, 2008

Lassen Volcanic National Park has several volcanoes, which include: Lassen Peak Chaos Crags

Mount Tehama (Brokeoff Mountain) And the remains of ancient Mt. Tehama, which erupted violently approximately 350,000 years ago, leaving only a collapse crater. crater rim ‘caldera’ Estimation of Mt Tehama Mapview of caldera rim

Today, Lassen exhibits another feature of volcanic regions: an active hydrothermal system. Hotspring at Devil’s Kitchen hydrothermal area is this way Bumpass Hell hydrothermal area Little Hot Spring Creek Sulphur Works Hot Springs

The hydrothermal system is visible on the surface in the form of hot springs and fumaroles Hot spring: area where hot water emerges from the Earth Fumarole: vent thru which hot gases escape

Hydrothermal systems form in parts of the Earth’s crust where there is water and heat. precipitation (rain, snow) streams groundwater magma magmatic heat Springs, fumaroles water heat

At Lassen, the heat comes from the magma stored deep beneath the volcano, precipitation (rain, snow) streams groundwater magma magmatic heat Springs, fumaroles water heat

and the water comes from rain and snowmelt that infiltrates into the soil and underlying crust. precipitation (rain, snow) streams groundwater magma magmatic heat Springs, fumaroles water heat

precipitation (rain, snow) magma degassing streams groundwater magma Hydrothermal Circulation magmatic heat & H 2 O, CO 2, HCl, H 2 S volatiles: Springs, fumaroles water heat In addition to picking up heat, the circulating groundwater picks up volcanic volatiles that have escaped the magma. volatiles

Fe Si This volatile-rich water reacts with crustal rocks as it rises to the surface in the hydrothermal circulation zone.

The chemical and physical properties of the heated water and volcanic volatiles results in the hydrothermal features we see around Lassen.

Hydrothermal areas are located in three main areas: Inside the ancient caldera South of the park Warner Valley

In the Lassen Astrobiology Intern Program, we’re going to be working in Warner Valley. Warner Valley

Lake Almanor View of Warner Valley to the southeast from above Lassen Peak.

Lassen Peak Bumpass Hell Warner Valley Map-view of Warner Valley

And although it is not clear from satellite imagery, when we overlay a geologic map… Warner Valley

we can see what rock is exposed on the Earth’s surface in this area. Warner Valley

We can see that Lassen and Warner Valley are composed of different geologic units. Each of these colors represents a different unit Warner Valley

Each of these geologic units are composed of a rock of a particular relative age and chemical composition. Each of these colors represents a different unit Warner Valley

Basalt/Basaltic Andesites (Sifford Mtn.) Andesites (Dittmar Volcanic Ctr.) Andesites (Dittmar Volcanic Ctr.) Dacite (Flatiron Ridge) Dacite (Panther Creek) Dacite (Bumpass Mtn.) Warner Valley field area Dacite (Bench Lake) glacial till Around Warner Valley, there are a variety of volcanic rocks and glacial sediments.

Basalt/Basaltic Andesites (Sifford Mtn.) Andesites (Dittmar Volcanic Ctr.) Andesites (Dittmar Volcanic Ctr.) Dacite (Flatiron Ridge) Dacite (Panther Creek) Dacite (Bumpass Mtn.) Warner Valley field area Dacite (Bench Lake) glacial till The names dacite, andesite, and basalt, describe volcanic rocks of a particular chemical composition and grain size.

Basalt/Basaltic Andesites (Sifford Mtn.) Andesites (Dittmar Volcanic Ctr.) Andesites (Dittmar Volcanic Ctr.) Dacite (Flatiron Ridge) Dacite (Panther Creek) Dacite (Bumpass Mtn.) Warner Valley field area Dacite (Bench Lake) glacial till The white ‘glacial till’ units indicate areas filled with sediment deposited by glaciers.

We will be visiting several sites in Warner Valley on our fieldtrip. Warner Valley Campground SpringsDevil’s Kitchen

This map tells us more than just rock type, it also indicates: faults topography creekshot springs elevation

We will be using this type of map in the field to locate where we are and determine additional information about our fieldsites, utilizing work done by scientists before us.

Now for a few Questions: Can you locate the Warner Valley Campground, Drakesbad, and Devil’s Kitchen on Google Maps? In what geologic units are our fieldsites? *Bonus* What geologic units might exist beneath the surface deposits at our fieldsites in Warner Valley?