Presentation on theme: "How did Block Island form? How is it changing now? What will it look like in the future?"— Presentation transcript:
How did Block Island form? How is it changing now? What will it look like in the future?
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)
Wind Erosion Wind: erodes land by carrying away rock particles mostly smaller particles: sand and rock dust (silt and clay) are carried by wind
Wind Deposition deposition by wind: most common – dunes (mounds of wind-blown sand) gentler slope of a dune – faces wind
Slumping: erosion from groundwater and gravity Large block falls off a cliff or bluff forms- sea cliffs/bluffs
Erosion by ocean waves physical weathering: force of the water weathers and erodes the shoreline affecting beaches
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
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??
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??
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:
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: e=active&safety_mode=true e=active&safety_mode=true
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
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
Glacial Deposits glacial till: unsorted glacial materials stratified drift: sorted and deposited in layers by meltwater Glacial erratic
Features from glacial deposition: Glacial moraines: landforms made from glacial till terminal (end) moraine: deposited at the end
More features from glacial deposition: moraine erratics: large boulders transported by glaciers
More Glacial Deposition features drumlins: low tear- shaped mounds of till kettles: depressions left from melting ice
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
Your tasks in the field (gathering evidence for your big 3 questions)
Task 1: create a topographic map of Block Island
Converting an island into a “topo” map
Creating a Contour/Elevation Map Use your elevation observations to determine the higher/lower points on BI Draw contour lines onto the map
Try a sample map
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
Soil horizons, or strata
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
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
Task 3: create a beach profile Beach profiling provides clues as to: how the beach formed how is it changing now
General beach anatomy
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).
More of the same
Task 4: Measuring wind speed and direction Wind speed: use an anemometer Wind direction: use the compass
Good luck geologists!
Review: Fill in the characteristics for each type of change EROSIONDEPOSITION