Geology 150U/390T Field trips Page 8

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Pressure ridges in lava flow After visiting the crater floor, we hiked around the rim of the cinder cone. This view shows "pressure ridges" in Lava Flow Two as seen from above on the south rim of the cone.

Pressure ridges form when the top of a lava flow cools and becomes plastic. Liquid lava is still flowing underneath and internal pressures distort the surface perpendicular to the direction of flow, forming characteristic ridges in the surface which look like waves. Lava breaking through the cooling surface forms mounds called "squeeze ups", like those we saw at Dotsero.
Lava Flow Two, Capulin Volcano, NM.


Sierra Grande shield volcano From the SW rim, a view of the Sierra Grande shield volcano and Capulin lava flows. Sierra Grande is a huge feature, possibly the largest continental shield volcano on earth. Besides its size, Sierra Grande is unusual in that it is composed of andesitic lava, not basalt. Normally, andesitic lava is very viscous and forms steeper sided composite cones, not shield volcanoes.

In the foreground is an extension of Lava Flow Two and in the lower left area is a small section of Lava Flow One. Highway 64 runs across the image just below Sierra Grande.
Sierra Grande Volcano, near Capulin, NM


Lava flow 2 from above The crater of Capulin Volcano is asymmetrical; the eastern rim is several hundred feet higher than the western rim. This view across the crater shows the difference in altitude. See the next image for an explanation.
East rim looking west, Capulin Volcano, NM.


East rim flora While it may be difficult to see because of the ground slope, look carefully at the trunks of the trees. You should be able to detect a definite slant in them. The winds here at Capulin blow consistently out of the southwest and the trees are deformed due to the constant force of the wind. So, too, is the Capulin crater.

The wind picked up the ejected material and preferentially deposited it downwind; on the east side. Over many years, the east rim of the crater grew much higher than the west. Wind and water; two of the softest substances on earth, yet responsible for the majority of the landscapes on the earth's surface. The awesome power of patience and persistence.
East rim flora, Capulin Volcano, NM.


Leaving Capulin, we head west back towards Raton. A road cut exposes a layer of the Fort Hays formation rich in fossilized marine organisms. I found a nice ammonite impression here.

Folsom, NM is the namesake for the Folsom Man, an ancient American native whose fluted spear points and arrowheads were found mixed with now extinct bison bones near here. The discovery revolutionized the theories about Ice-Age inhabitants of the Southwest.
Road cut along highway 72, west of Folsom, NM.

So ends the field trip weekends. They were enjoyable and very informative. I'd like to do another one, but think I'll skip the webpages next time and concentrate on the geology. And keeping track of my film cannisters!

Thanks
I would like to thank Beth Simmons of the MSCD Geology Department for her advice and editorial assistance in the preparation of these webpages.

I would also like to thank my Father for his reviews and constructive criticisms. Thanks, Dad.

Last modified: 1/19/2004