Geology Introduction to Lassen and Warner Valley

WebcourseClick 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

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.

Lasse

n isway

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

Devil’s Kitchenhydrothermal areais this way

Bumpass Hellhydrothermal area

Little Hot Spring Creek

Sulphur WorksHot 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

HydrothermalCirculation

magmatic heat &

H2O, CO2, HCl, H2Svolatiles:

Springs, fumaroles

water

heat

In addition to picking up heat, the circulating groundwater picks up volcanic volatiles that have escaped the magma.

volatiles

Fe

Fe

Fe

Fe

Si

Si

Si

ACID

IC W

ATER

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

Warner Valley

Lake AlmanorView 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

topographycreekshot 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?