Geology Field Investigation - Parent Training Wellesley Elementary Schools - Wellesley Public Schools
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Geology Field Investigation
Parent Training
Wellesley Elementary Schools
Fall 2016
1
Training Objectives
• To provide background information for the
fourth grade geology field investigation
• To familiarize parent volunteers with
important geological sites in Wellesley
2
Presentation Outline
• Geology 101: Structure of the Earth
• Changes to the Earth’s Surface
• Wellesley’s geological sites
• Geology of Wellesley video
3
The Structure of the Earth
Crust: relatively cold, thin, brittle solid
fractures with earthquakes
made of calcium, sodium, and
aluminum silicate minerals
5-20 miles (8-32km) thick
thickest at mountains
thinnest at ocean floor
Mantle: an elastic solid
most of the earth’s mass.
made of iron, magnesium
aluminum, silicon, and oxygen
convection currents cause
crustal plates to move
1832° F (1000° C)
1800 miles (2896km) thick
Liquid outer core:
made of iron and sulfur
6692° F (3700° C)
1400 miles (2252km) thick
Solid inner core:
made of iron
remains solid due to immense
pressure and high heat
9000° F (5000° C)
800 miles (1287km) to center
4
Plate Tectonics
• Plate tectonics is the movement of the earth’s crustal plates due to convection currents in
the mantle
• As plates move they may collide, pull apart or rub past each other
• The earth’s land masses sit atop these crustal plates and are deformed by crustal motion
5
Stories in Stone
Every rock tells a story:
how it formed and
what has happened to it since
6
Changing Earth
• How do mountains shrink?
• How do boulders become small pebbles?
• How do sharp rocks become smooth and
rounded?
• What makes sand?
Answer?
7
Weathering
• Weathering: “breaking down” forces – things that break
rocks & minerals into smaller particles
• Physical
• Chemical
• Biological
8
Physical Weathering
rain, rivers, waves
and storms -
moving water greatest cause of
physical weathering
wind carrying pieces
wind of debris can sand-
blast surfaces
freezing/melting
temperature cycles-
(ice) water expands when it
freezes
9
Chemical Weathering
when oxygen reacts with
oxidation iron-rich minerals - rust
gases in the air (from
1908 1969 pollution or natural causes
acid rain such as volcanoes) mix
with rain, snow or other
precipitation
10Biological Weathering
organisms growing
lichens, on rocks produce
bacteria, acids and enzymes
that break down and
fungi dissolve the rock
trees
tree roots can break
and apart huge boulders
plants
11Photos courtesy of Irene Gruenfeld
12Erosion
• Erosion: “carrying away” forces – things that take the
broken off pieces and move them elsewhere
13Deposition
• Deposition: “leaving behind”–rock material is laid down
(volcanoes also leave new rock)
14Hemlock Gorge
• cave – rock material has
been worn away
15Sedimentary rock
• Made from sediments: bits and pieces of rock and organic
matter cemented and compacted together
• Rocks break apart and form sediments - weathering
• Sediments transported by wind, water, and glaciers - erosion
• Heavier material drops out first - deposition
• Layer upon layers, flat and parallel
• Weight of water compresses the layers
16Hemlock Gorge
• Around 580,000,000 years old
• Sedimentary – Roxbury
Puddingstone
• Large rounded rocks
embedded in sandstone
• Embedded rocks resembled
raisins in “pudding”
Similar rock is found in Africa!
17Hemlock Gorge
Roxbury Puddingstone
Is this an example of weathering, erosion or
deposition?
18Shaping New England
Glaciers
19Glacial Formations
• 22,000 years ago – peak of the Ice Age
• Glaciers covered New England
• Glaciers move – push rocks and earth aside
• Rocks get frozen in the ice and carried long
distances
• Receding glaciers and melting ice create
new landforms
20Abrasion and Plucking
• Glacier came from NW passing slowly over
bedrock
– Polishing the surface
– Scraping in the rock – glacial striations
– Plucking the backside
21Devil’s Slide St Mary’s Cemetery
22Different Types of Rock
23Intrusions
• Magma under the surface
is pushed up into any
available cracks and
spaces in existing rock
• Can vary from mountain-
range-size to vein-like
fracture fillings
24Devil’s Slide
• 600,000,000 years old
• Oldest rocks in Wellesley
• Formed deep below the surface
• Diorite intrusion into surrounding
granite
• Millions of years of weathering for
our granite and diorite to become
exposed at the surface
25A Volcano?
in Wellesley?
26Volcanic Breccia
• As lava moves up through cracks
in bedrock, pieces of bedrock
break off
• Bedrock pieces show signs of
stretching from the heat
• Some lava never reaches the
surface - cools slowly, hardening
underground with pieces of
bedrock embedded in it
• Over time, the volcano has
eroded away – only plug remains
27St. Mary’s Cemetery
• 580,000,000 years old
• Igneous – volcanic breccia
• Hardened lava that never
made it to the surface
• More breccia is found near the school in nearby
Needham – it was a large volcano
28Devil’s Slide St Mary’s Cemetery
Are these examples of weathering, erosion
or deposition?
29Eskers
• Ridges of gravel and sand
• Rivers and streams flowed on, in and beneath
glaciers
• Can be over 100 ft. high, hundreds of feet
wide, and several miles long
30Longfellow Pond – Esker Trail
31Glacial Erratic
Kelly Memorial Park
• Erratic: a rock that differs
from native rock in size and
type
• Carried by glacial ice, often
hundreds of miles
Note: Fairy Rock has very large pink feldspar crystals
(this tells us it cooled very slowly below the surface)
32Longfellow Pond Kelly Memorial Park
Esker Trail Glacial Erratic
Are these examples of weathering, erosion
or deposition?
33Kelly Field: Kettle Hole
• Formed by a retreating (melting) glacier
• Blocks of ice break off, getting surrounded by sand,
gravel and rocks from the melting glacier
• Blocks eventually melt leaving a depression
34Weathering & Erosion
• Devil’s Slide
– trees growing into the rock
- lichen growing on the rock
- rocks broken off the backside
• St. Mary’s Cemetery
- channel cutting across the rock
- signs of rocks eroding at different rates
• Hemlock Gorge
- the cave formed by water
- rocks falling out
35Glaciers
• Devil’s Slide • St. Mary’s Cemetery
- smoothing on front - smoothing on front
- glacial striations - glacial striations
- plucking on back - plucking on back
• Longfellow Pond • Kelly Field
- esker - glacial erratic
- kettle hole
36The Geologic Time Scale
a trip through Wellesley’s geologic history
37Final thoughts:
• Stories in Stone: every rock tells a story of how it formed
and what has happened to it since
• Understand what a rock, or rock formations, tell you about
the geologic history of the area (i.e. glacial activity,
volcanic activity, crustal motion, water action)
• Don’t worry about specific rock names but perhaps look for
identifying traits for each type of rock:
igneous – visible crystals
sedimentary – layers, fossils, rounded particles
• Generate excitement and curiosity as you learn about
Wellesley’s history through its rocks, exploring it’s
volcanic past, glacial past and present day geology
38You can also read
