Weathering profile of Volcanic Tuff

1. Weathering profile of Volcanic Tuff www.AssignmentPoint.com

2. Weathering profile of volcanic tuff in a road cut after five years of exposure to weathering processes.

3. Weathering profile of volcanic tuff in a road cut after fifteen years of exposure to weathering processes. Note that rills have developed over time where surface runoff has flowed down the face of the road cut.

4. Weathering profile of volcanic tuff in a road cut after twenty-five years of exposure to weathering processes. Note that sharp edges are now rounded and the profile is stained red.

6. Physical or mechanical weathering includes weathering processes that cause rock or sediment to break down into smaller pieces without changing the chemistry (mineralogy) of the rock. The image on the left demonstrates how freezing water can exert high stresses as it expands, causing the glass jar to break. Water trapped in micro-cracks within rock can expand during freezing cycles and exert tremendous stresses to the crack wall and cause rock to break apart.

7. Freeze-thaw cycles in this alpine environment are responsible for the break-up of this granitic bedrock by frost wedging. Freeze-thaw cycles are also important in subpolar environments where temperature fluctuate around the freezing isotherm (0° C).

8. Root penetration, such as that exhibited by this small lodgepole pine, can exert great pressures within joint cracks as the tree grows and the roots begin to expand.

9. Chemical weathering processes cause changes in the mineralogy of rock. A marble tombstone engraved in 1970 is subjected to chemical weathering.

10. Over time the calcium carbonate (CaCO3) will dissolve by solution weathering to form calcium (Ca+2)and bicarbonate (HCO3-1) ions causing the 1820 engraving to disappear.

12. Production of carbonic acid and bicarbonate ions H2O + CO2 H2CO3 H1+ + HCO31-

13. Hydrolysis reactions involve hydrogen ions (H+1) derived from carbonic or other acids within the environment. Hydrolysis reactions can convert primary feldspars in rock to clay minerals, such as kaolinite. Eocene oxisol, Ione, CA Iron oxide laterite (red) overlies kaolinite clay (white). Formed on alluvium derived from eroded Sierra Nevada volcanics in a tropical climate 38 m.y. ago.

14. A Horizon Oxidation Reactions Goethite B Horizon (goethite yellow precipitate and hematite red precipitate) 4FeO + 2H2O + O2 2FeOOH Dehydration to form Hematite 2FeOOH Fe2O3+ H2O Modern soil formed in laterite of Eocene Ione Formation

16. Rills form from solution weathering of limestone. Compare the depth of rilling on the subsequent two slides.

17. If environmental factors are held constant what factor will explain greater weathering?

18. Terminal zone of melting glacier.

19. Recessional moraine loop within Chiatovich Valley, CA. How could you infer the relative age of glacial moraines from weathering properties of surface boulders?

20. Solution weathering of limestone results in hummocky topography (see inset slide). Sinkholes form as acidic groundwater dissolves the underlying carbonate rock. Roofs of caves can collapse when underlying support is removed by solution weathering.

21. The formation of stalactites and stalagmites in limestone caves demonstrates that dissolution of calcium carbonate (calcite) is a reversible process. Environmental factors such as changes in water temperature, acidity, changes in pressure can all influence the solubility of calcium carbonate in solution. The image was taken from Carlsbad Caverns, New Mexico.

22. Minerals weather at different rates. The plagioclase crystals stand in relief because they are more resistant to chemical weathering processes than the mafic minerals that are oxidized.

24. Classic examples of differential weathering are prevalent throughout the southwestern United States. These monuments and mesas are capped with resistant quartzite. The weaker sandstone and shale are being eroded by fluvial and mass wasting processes.

26. Soil Forming Factors (Clorpt) Climate Organisms Relief Parent material Time

27. Note that climate plays a major role in the depth of the B horizon (zone of accumulation) or illuvial zone.

28. Vegetation can play an important role in soil nutrient replacement and pH.

30. Soil development on 75,000 and 150,000 year old moraines. As soils age the soil profile becomes thicker, redder, and clay content increases.