Presentation on theme: "How did Block Island form. How is it changing now"— Presentation transcript:
1How 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?
2Block Island: a product of Erosion and Deposition weathering: the change/breakdown of rock on Earth’s surfaceerosion: movement or transportation of weathered materialsagents of erosion: gravity, wind, glaciers, and water (ocean currents and waves, streams, groundwater)deposition: the leaving behind of materials carried by erosionagents of deposition: gravity, wind, glaciers and water (same as for erosion)
4Wind Erosion Wind: erodes land by carrying away rock particles mostly smaller particles: sand and rock dust (silt and clay) are carried by wind
5Wind Depositiondeposition by wind: most common – dunes (mounds of wind-blown sand)gentler slope of a dune – faces wind
6Slumping: erosion from groundwater and gravity Large block falls off a cliff or bluffforms- sea cliffs/bluffs
7Erosion by ocean wavesphysical weathering: force of the water weathers and erodes the shoreline affecting beaches
8Ocean Wave Depositionbeaches: deposits of sand or larger particles on ocean (or lake) frontbeach 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
9Wave anatomy Wavelength: distance between 2 crests or 2 troughs Wave height (2 X amplitude): height from trough to crestHow could you determine these??
10Wave characteristicsWave period: the time is takes for a wave to pass a fixed pointWave frequency: the number of waves that pass by in a given time.How could you determine these??
11Wave characteristics 2Wave speed: the distance traveled by a given point on the wave (such as a crest) in a given interval of time. In equation form:
12Longshore Currentsgeneral movement of sand along beach: in same direction that waves hit shorelongshore current: movement of water and sediment parallel to, and near shorelineanimation:Real video:
13Features from longshore current deposition: Headland: land surrounded by water on three sidesspit: long narrow deposit of sand connected at one end of shoretombolos: ridge of sand deposits connecting islands to mainland
14Glacial ErosionGlaciers are “rivers of ice” slowly flowing, moving sediments and changing the surface and shape of the ground beneath itLast glacial ice age in NE ended about 18,000 years ago
15Glacial Deposits glacial till: unsorted glacial materials stratified drift: sorted and deposited in layers by meltwaterGlacial erratic
16Features from glacial deposition: Glacial moraines: landforms made from glacial tillterminal (end) moraine: deposited at the end
17More features from glacial deposition: moraineerratics: large boulders transported by glaciers
18More Glacial Deposition features drumlins: low tear-shaped mounds of tillkettles: depressions left from melting ice
19Stratigraphy 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
20Your tasks in the field (gathering evidence for your big 3 questions)
21Task 1: create a topographic map of Block Island
27Task 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 claySieving Purpose: this tells how the soil got there
30Sand, 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 mmfine mmmedium mmcoarse mmvery coarse mm
31Conclusions 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 erosionThis makes them less stableFlat, small particle beaches are formed from gentle deposition forces, and are more stable
32Task 3: create a beach profile Beach profiling provides clues as to:how the beach formedhow is it changing now
35How 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).