# Presentation: 936990

## Module 18 – HUMDINGER EXAM

- OUTWASH or GLACIAL TERRACE
- Bt horizon
- The Take Home Exam

- 1 to 1:30 PM Friday 10/24/08

## 1. INCREASE THE SEDIMENT  LOAD. GIVEN SUFFICIENT TIME, THE STREAM  SLOPE WILL INCREASE. 

**1. INCREASE THE SEDIMENT  LOAD. GIVEN SUFFICIENT TIME, THE STREAM  SLOPE WILL INCREASE. **

**2. AT A THRESHOLD SLOPE OF 0.016 FT/FT FOR 0.15 CFS STREAM – OVER the threshold is a BRAIDED & under a MEANDERING stream (Schumm and Kahn, 1972)**

## 3. GENERALLY BRAIDED STREAMS “AGGRADES” OR BUILD S UP A VALLEY OR FLOODPLAIN. 

**3. GENERALLY BRAIDED STREAMS “AGGRADES” OR BUILD S UP A VALLEY OR FLOODPLAIN. **
**4.** **Braided streams associated with drier climates and glaciers.**
**5. Platt River 8 mi/hr and Missouri above the Platt 3 mi/hr or less (Lewis and Clark)**
**6. HUMDINGER OCCURS IN AN OUTWASH TERRACE.**

## LOUISIANA – Baton Rouge Area

- Soil had features of accumulation of iron and calcium much in excess of expected. Soil had a poorly expressed Clay accumulation in the B-horizon. The pH was neutral.
- JLR’s interpretation based on morphology and data was that this soil was in a discharge site.
- Challenge: We were miles from the Mississippi River and other obvious water sources.
- Additional data: The well 30 m away was an artesian well without a pump.
- HOW CAN THIS HAPPEN???

## Bt-Horizon (Soil Taxonomy, 1975)

- 1. Distinct dry season
- 2. Takes time to form
- 3. Forms faster with Na present and formation is retarded with abundant Ca  or exchangeable Al present (helps to be leached and acid but not extremely so )
- 4. Dispersion of clay an important process
- 5. Dispersion of clay hindered by multi-valent cations (Ca, Al)

## Bt-Horizon (Soil Taxonomy, 1975)

- 5. Dispersion of clay often occurs when abundant water dilutes cations in the soil
- 6. Dry soils when first wetted disperse most easily for this reason and trapped air action
- 7. Dispersed clays move from attached conditions to suspended conditions in an initially saturated condition.
- 8. This water, with the suspended load, moves downward in macropores.
- 9. The peds are micropores and are relatively dry; water moves from the large pores by matric flow;
- 10. Clay is left on the ped surfaces forming clay skins.

## TILL SOILS IN SUB-HUMID ND

**Btn**

**Btg**

- Bw

- Bt

-  A
- E

- SODIC               PRAIRIE           FOREST

- RECHARGE WETLAND
- PRAIRIE POTHOLE SOIL

## OUTWASH TERRACE; HIGH WATER TABLE EVERY SPRING; 94% SAND OR COARSER, HIGH SODIUM & pH; white Bk is Protodolomite; note the Btn horizon. 

- E
- Btn pH 9.1
- Bkg

**50% clay**

- THE PARTICIPANT WILL DESCRIBE AND EXPLAIN THE DEVELOPMENT OF THIS SOIL, ESPECIALLY FOCUS ON THE WATER DYNAMICS.
- STIRUM: COARSE-LOAMY, MIXED, SUPERACTIVE, FRIGID TYPIC NATRAQUOLL

- 2Cg 94% sand

**OUTWASH TERRACE; HIGH WATER TABLE EVERY SPRING; 94% SAND OR COARSER, HIGH SODIUM & pH; white Bk is Protodolomite; note the Btn horizon. **

- 32

- Photo JL Arndt

## Concepts to use in your answer

- Matric flow a) wet to dry; b) frost (mod11);
- Saturated flow above and below water table;
- Formation of a Bt, Btn and Bk in terms of hydrology;
- Dispersion; translocation; reverse translocation;
- Braided stream; terrace;
- Evaporite sequence – alkaline branch
- Redoximorphic features