CH15 Glaciers and Erosion Mrs. Kummer Fall, 2014

Chapter Objectives Glaciers as Moving Ice – How they form – How they are classified – How they move – What features they have Glaciers help make stuff – Erosion – Deposition – Making of Lakes Ice Ages – Climate During Ice Ages – Glacial Periods – Causes of Ice Ages

Glaciers as Moving Ice Glacier: Masses of moving ice by compacting many many many many snowflakes How do Glaciers Form? Snowflakes fall  continues year round year after year  snowflakes compress to a snowfield as it accumulates  top layers melt and refreeze over and over with daily sunlight  snow crystal changes to firn on top layer  top layer too heavy now so it pushes down and squeezes air out of crystals/ice grains  no more white color, mostly steel blue  piles up and up until it is so heavy it starts moving downslope

Glaciers as Moving Ice So it looks like:

Glaciers-Vocabulary Snowline: elevation where above this line, the snow and ice survive year round Snowline: elevation where above this line, the snow and ice survive year round – Varies where you are on the globe: Equator: snowline is at 5500m above sea level Poles: snowline is at sea level Colorado for Rockies: 2800m – The snow above a snowline makes a snowfield: almost motionless mass of permanent snow and ice

Glaciers-Vocabulary Contd

What do Glaciers Look Like? Perito Moreno Glacier in Argentina

What Do Glaciers Look Like?

Glaciers: How Do They Live? Glaciers can grow as long as new snow is added faster than it melts, evaporates, or breaks off at the sea as icebergs Obviously, highly dependent on the Water Cycle According to USGS (U.S. Geological Survey), ~68% of our freshwater supply is captured in glaciers Only ~10% of the Earth’s surface is covered by glaciers at this time

Types of Glaciers Two main types of glaciers, named by where they are formed 1.Valley Glacier-Found in mountainous areas in the valleys between mountain peaks 2.Continental Ice Sheets-Found covering large land areas in Greenland and Antarctica ONLY

Types of Glaciers-Continental Ice Sheets In Greenland and Antarctica, they cover millions of square km Antarctica is covered by the largest ice sheet on Earth…1.5X as large as USA, and its thickest sections are 4000 m thick Greenland is 90% covered by glacial ice sheets…it is ¼ the size of USA, and its thickest sections are 3000 m thick If these ice sheets were to melt completely, it would raise sea levels by 60m everywhere

Glaciers-How Do they Move? Two main ways: Basal Slip Internal Plastic Flow Amount of movement is all over the place: On average, move 100m/year Faster ones move a km or more/year (Greenland’s Jakobshavn Glacier) Slower ones move a few cm/year (several continental ice sheets in Antarctica)

Glaciers-How Do They Move? Basal Slip Just like you saw the sand stick to the bottom of your ice block, a glacier starts melting where it is in contact with ground The melted ice hydroplanes on the watery bottom surface, to reduce friction between glacier and ground Glacier starts moving by slipping at the base

Glaciers-How Do They Move? Internal Plastic Flow Solid ice crystals slip over each other= internal plastic flow Scientists have staked glaciers to show movement The middle moves fastest due to higher friction on the sides from the rock walls

Features of Glaciers Crevasses-Large crack (30m deep) Icebergs-large chunks that break off of a glacier and float in the ocean

Features of Glaciers

Glaciers Help Make Stuff Three ways Glaciers make stuff: 1.Glacial Erosion 2.Glacial Deposition/Till Deposits 3.Glacial Lakes Many of these items were formed by glaciers melting in our last ice ages 10,000-15,000 years ago

Glacial Erosion

Glacial Deposition-Moraines

Glacial Deposition-Erratics Olmsted Point in Yosemite National Park, California

Glacial Deposition in Michigan A large moraine is present right around here…. Farmington Hills Bloomfield Hills Rochester Hills Auburn Hills

Glacial Lakes-The Great Lakes Early Ice Retreat: water drained to the south, lakes were HUGE Late Ice Retreat, Causing major Uplift in land – More land present, less water – Drainage changed from South to Southwest Today’s Great Lakes – More land exposed, creating UP – Drainage changed to draining NE to St Lawrence River

Glacial Lakes-The Great Lakes

Salt Lakes Made By Glaciers Lakes out in SW part of USA were formed by melting ice sheets But they had no outlet/connection to other bodies of water Region is dry with little precipitation So, heavy evaporation leaves the lakes very small and very salty Ex. Great Salt Lake was HUGE Lake Bonneville- the size of UTAH

Ice Ages-Objectives Objectives: – Climate During Ice Ages – Glacial Periods – Causes of Ice Ages What is an ice age? Long period of climatic cooling during which continental ice sheets cover large areas of the earth’s surface How many ice ages has Earth had? Many/Several: At least 4 have documented evidence Last Ice Age was 10,000-15,000 years ago

What Starts and Ice Age?  “You Will Need:” – An average global temperature decrease of 5°C – Increase in snowfall  Ice ages also have cycles with warming and cooling periods -Glacial Period: Time when Ice Sheets grow/advance -Interglacial Period: Time when warmer temps allow ice sheets to retreat slightly

What Causes an Ice Age? Many theories, now including climate change One theory is typically accepted by scientists Milankovitch theory, named for Milutin Milankovitch, a Serbian Scientist

Milankovitch Theory M. Theory: Regular changes in the Earth’s orbit around the sun and the tilt in the Earth’s axis – Shape of Earth’s orbit (our revolving) changes from circular to elongated/elliptical back to circular every 100,000 years – The tilt in the Earth’s axis varies between 21.5° to 24.5° – Circular motion of the Earth’s axis (our spinning) – The axis completes a full circle every 26,000 years

Evidence of Milankovitch Theory Ocean Floor remnants-shells are found in layers of sediment that support a repeated heating and cooling period following Milankovitch’s timelines Specifically, the ratio of 2 isotopes of O 2 in the shells of these marine animals is related to the temperature of sea water when the animals lived