Basalt, a type of igneous rock, is one of the most common rocks found on the planet. Igneous rocks (derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava and many times includes gaseous inclusions called vesicles.
15 minute walk on well maintained trail from good parking w/ toilet access at Crag Crest Trail-head
Across Grand Mesa you will see numerous basalt boulder fields. These fields are a result of deterioration of the lava cap by various means such as “slump block failure” or “mass wasting”. As you walk the Crag’s Crest Trail you will see several of these basalt boulder fields. Note the texture of the basalt rock. The numerous small holes, or vesicles, in the basalt boulders were formed by gas bubbles trapped in the lava when it cooled and solidified. This rock is called vesicular basalt. In some boulders, elongated vesicles formed when the gas bubbles were stretched as the lava continued to move during cooling.
Basalt is the most abundant of all igneous rocks. Compared to other types of volcanic rocks, basalt has a lot more magnesium and iron in it, which gives it a darker color. Many basalt eruptions have a lot of dissolved gases in the lava…sort of like the bubbles you see in a glass of soda or mineral water. Most of the dissolved gas in a lava flow is water vapor (steam), but other gases like carbon dioxide or hydrogen sulfide are common as well.
We would like to acknowledge the support of the rangers at the Grand Mesa National Forest Visitor Center, in particular the resident geologist, Mike Wiley.
You may log your find immediately but to complete the process you must answer the following questions and e-mail them at the same time to TEAM kekj . Please do not post the answers in your log: It will be deleted!
1. Can you find both rounded and elongated vesicles in the boulders in this area?
2. Which type is most prominent in GZ area?
3. What is the approximate size of the largest vesicle you observed at GZ area? OR as an OPTION: Take a photo of the largest vesicle with your GPS beside it for perspective and post it to the web site.
CO-FTF Congrats go to Rojo464 and Pauleefox on 10-7-14
Additional Waypoints
P15D7GE - Parking
N 39° 02.505 W 107° 59.913
Vesicular Basalt - full of HOT AIR!
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