GLY433/533                                                   SEM Laboratory
                                  Pyroclastic Rocks

Part I: Introduction to the Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer
(EDS) by Peter Bush, director of the laboratory

        Electron optics
        Interaction of electron beam with specimen
        Secondary electrons
        Backscattered electrons
        X-rays
        Auger electrons
        Energy dispersive spectrometer (EDS)
        Wave-length dispersive spectrometer (WDS)

Part II: Sample inspection and preparation. The purpose of this exercises is to give you some
experience in:

        a. Stereo microscope viewing
        b. Sample labeling
        c. Carbon coating

Samples of tephra from four samples representing different classic eruptions are mounted on a stub for
SEM viewing and analysis. Carefully examine some unmounted grains with a stereo microscope and
describe the grain characteristics (and identify if possible) in your notebook. The mounted grains have
been photographed before carbon coating and this image will be available for you to use as a map.

The samples are:

        a. COT-0301A Cotopaxi ??
        b. MSH-8405 Mount St. Helens 1980
        c. Pompeii  flow 2, Vesuvius AD 79
        d. PEL-8816 Pelee May 8, 1902

Part III: Introduction to the instrument

Click here to see the various instruments in the South Campus Instrument Center.
The techniques that you will practice today include:

        a. Loading the sample
        b. Viewing the sample
        c. Saving the image
        d. Making an EDS analysis

Part IV: Hands-on SEM analysis of the pyroclasts that you mounted

        a. Examine each particle from the four samples with the SEM
        b. Choose an appropriate magnification and make a digital image of each grain
        c. Use the EDX to get a general composition of the various particles and
        sub-particles.
        d. For the appropriate grains describe their bubble structure and microlite texture.
        Then make an interpretation of the features that you see in terms of eruption
        dynamics in the conduit. All of the examined images and data will be available
        on the web site for analysis following the lab.

Part V. Viewing the samples examined in the lab.

All of the samples examined in the lab are available in a file that you can access by clicking on the buttons.

a. Cotopaxi, Plinian fall
b. Mount St. Helens 1980, pyroclastic flow
c. Vesuvius AD 79, pyroclastic flow
d. Pelee May 8, 1902, nuee ardente

Part VI: Homework exercise on “unknown” grains

You have available data from a single stub divided into four areas. Each area contains five grains
selected to show a variety of types from their sample and deposit. These four stub areas represent four
unique deposits:

        1) 1888-90 Vulcanian deposit of Vulcano, Sicily
        2) 1906 blast deposit of Ksudach Volcano, Kamchatka
        3) 1964 debris flow of Shiveluch Volcano, Kamchatka
        4) 1965 surge beds of Surtsey Volcano

You can view the images and their EDX spectra in the Image file. In the week following your
laboratory work you should analyze this data make a report giving your results. Besides the identification
of each particle you should identify which area on the stub is occupied by each of the four deposits listed
above. Please give the reasoning for your conclusions.