Local Geology
At this area you are seeing parts of the Bolivar-Mansfield Tectonic Zone.
“The Bolivar-Mansfield Tectonic Zone (BMTZ) is an early Proterozoic basement structure that trends northwest through the Midcontinent region. This structure was reactivated several times during Precambrian and Paleozoic time.” (Cox )
- Early Proterozoic =541 – 2500 million years ago
- Precambrian = 541 – 4600 million years ago
- Paleozoic = 252.2 – 541 million years ago
Earthquakes:
Different types of Faults
A close look at faults helps geologists to understand how the tectonic plates have moved relative to one another.
Normal faulting – where the crust is being pulled apart, normal faulting occurs, in which the overlying (hanging-wall) block moves down with respect to the lower (foot wall) block.
Reverse faulting – where the crust is being compressed, reverse faulting occurs, in which the hanging-wall block moves up and over the footwall block – reverse slip on a gently inclined plane is referred to as thrust faulting.
Dip-slip movement—Slip of one fault block, relative to the other block, by movement parallel to the dip of the fault. On any inclined surface, such as a fault in the Houston area, it is possible to draw an imaginary horizontal line, termed the strike of the fault, and to draw a second line perpendicular to the strike, termed the dip line. The angle by which the dip line deviates from horizontal is the dip of the fault; it corresponds to the inclination of the fault in nonscientific terms. If movement of one fault block relative to the other block occurs parallel to the dip line, it is termed dip-slip movement.
Downthrown side—The side of a fault that appears to have moved downward relative to the other side.
Upthrown side—The side of a fault that appears to have moved upward relative to the other side.
(USGS)
Nature’s crusher
Fault gouge is crushed and ground-up rock produced by friction between the two sides when a fault moves. (USGS)
Source: Web
Types of Erosion:
Splash Erosion: Small soil particles are detached and sent airborne through the impact of raindrops on soil.
Sheet Erosion: Raindrops break apart the soil structure and it's moved down-slope by water that flows overland as a sheet rather than definitive channels. This occurs frequently during cloud bursts.
Rill Erosion: This process develops small, short-lived, concentrated flow paths. These paths create a sediment source and delivery system for hill-slope erosion. Areas where precipitation rates exceed soil infiltration rates are more prone to this type of erosion.
Gully Erosion: Water flows in narrow channels during or directly following heavy rains or melting snow. The gullies can erode to considerable depths.
Valley or Stream Erosion: Continual water flow alongside land (along a linear feature) creates this type of erosion. It extends downward, deepening a valley, and head-ward, extending the valley into the hillside. This occurs most frequently in times of flooding.
Bank Erosion: Over time, banks of rivers and streams are naturally worn down.
Freezing and thawing: Cold weather causes water trapped in tiny rock cracks to freeze and expand, breaking the rock into several pieces.
Wind erosion: is of two primary varieties: deflation, where the wind picks up and carries away loose particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind.
Attrition is where particles/seaload carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as shingle and sand.
**Logging requirements**
DO NOT POST ANSWERS IN YOUR LOG.
Send the following answers to me via email.
- The text "GC5EY5Q 38’s Special" on the first line
- How many fault lines are there?
- What type of fault lines are here?
- Looking at the south east end of the rock formations, what kind of sediment lines are here? (1=straight, 2=vertical, 3=wave, 4=breccia)
- What is the #1 type of erosion happening here? (1=Splash Erosion, 2=Wind erosion, 3=Freezing and thawing, 4=Attrition)
- How tall is this cliff?
- Is there any fault gouge present between the fault lines?
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