1. How did Block Island form. How is it changing now
How did Block Island form? How is it changing now? What will it look like in the future?

2. Block Island: a product of Erosion and Deposition
weathering: the change/breakdown of rock on Earth’s surface
erosion: movement or transportation of weathered materials
agents of erosion: gravity, wind, glaciers, and water (ocean currents and waves, streams, groundwater)
deposition: the leaving behind of materials carried by erosion
agents of deposition: gravity, wind, glaciers and water (same as for erosion)

3. Background Information

4. Wind Erosion Wind: erodes land by carrying away rock particles
mostly smaller particles: sand and rock dust (silt and clay) are carried by wind

5. Wind Deposition
deposition by wind: most common – dunes (mounds of wind-blown sand)
gentler slope of a dune – faces wind

6. Slumping: erosion from groundwater and gravity
Large block falls off a cliff or bluff
forms- sea cliffs/bluffs

7. Erosion by ocean waves
physical weathering: force of the water weathers and erodes the shoreline affecting beaches

8. Ocean Wave Deposition
beaches: deposits of sand or larger particles on ocean (or lake) front
beach changes seasonally – remember beach profile??
berm: top of the sloping surface (above is part for recreation)
sand bar: long underwater ridge of sand carried away from beach

9. Wave anatomy Wavelength: distance between 2 crests or 2 troughs
Wave height (2 X amplitude): height from trough to crest
How could you determine these??

10. Wave characteristics
Wave period: the time is takes for a wave to pass a fixed point
Wave frequency: the number of waves that pass by in a given time.
How could you determine these??

11. Wave characteristics 2
Wave speed: the distance traveled by a given point on the wave (such as a crest) in a given interval of time. In equation form:

12. Longshore Currents
general movement of sand along beach: in same direction that waves hit shore
longshore current: movement of water and sediment parallel to, and near shoreline
animation:
Real video:

13. Features from longshore current deposition:
Headland: land surrounded by water on three sides
spit: long narrow deposit of sand connected at one end of shore
tombolos: ridge of sand deposits connecting islands to mainland

14. Glacial Erosion
Glaciers are “rivers of ice” slowly flowing, moving sediments and changing the surface and shape of the ground beneath it
Last glacial ice age in NE ended about 18,000 years ago

15. Glacial Deposits glacial till:  unsorted glacial materials
stratified drift:  sorted and deposited in layers by meltwater
Glacial erratic

16. Features from glacial deposition:
Glacial moraines: landforms made from glacial till
terminal (end) moraine: deposited at the end

17. More features from glacial deposition:
moraine
erratics: large boulders transported by glaciers

18. More Glacial Deposition features
drumlins: low tear-shaped mounds of till
kettles: depressions left from melting ice

19. Stratigraphy Stratigraphy is the study of strata, or layers
Stratigraphy can tell us about how the soil was deposited, they are clues to the land’s origin

20. Your tasks in the field (gathering evidence for your big 3 questions)

21. Task 1: create a topographic map of Block Island

22. Another look

23. Converting an island into a “topo” map

24. Hawaii topo

25. Creating a Contour/Elevation Map
Use your elevation observations to determine the higher/lower points on BI
Draw contour lines onto the map

26. Try a sample map

27. Task 2: Sieving soil, to tell particle size
You will collect soil samples to sift with “sieves”
These will separate the soil into different sized particles – gravel, fine gravel, coarse sand, fine sand and silt and clay
Sieving Purpose: this tells how the soil got there

28. Soil sizes

29. Soil horizons, or strata

30. Sand, different sizes deposit by different ways
How is sand classified? If you classify sand by size, you look at the diameter of each sand particle. Very coarse sand, like you might see in a sand box, has the largest particles. The diagram below shows the actual size of sand particles from 0.5 to 2 mm in diameter.
very fine   mm
fine   mm
medium   mm
coarse   mm
very coarse   mm

31. Conclusions from sieving and soil profiling:
The bigger the sand particle size, the steeper the beach typically is:
Steep, big particle beaches are formed from strong deposition forces and erosion
This makes them less stable
Flat, small particle beaches are formed from gentle deposition forces, and are more stable

32. Task 3: create a beach profile
Beach profiling provides clues as to:
how the beach formed
how is it changing now

34. General beach anatomy

35. How does the beach change over time?
The shape of the beach is in continual change due to the weather and tides.
In calmer weather with regular tides, sand is gradually deposited onto the beach from sand bars out in the ocean, dunes and berms may form.
In stormy weather, the beach erodes and sand is brought from the beach to sand bars, which run parallel to the shore (provides better surfing).

36. More of the same

37. Task 4: Measuring wind speed and direction
Wind speed: use an anemometer
Wind direction: use the compass

38. Good luck geologists!

39. Review: Fill in the characteristics for each type of change
EROSION
DEPOSITION