1

DESERT DUST

• YOU HAVE A HANDOUT THAT PROVIDES AN OVERVIEW OF THE SUBJECT – READ IT AS WELL AS MY BRIEF SUMMARY

• DUST STORMS COMMON PHENOMENON IS ARID AND SEMI-ARID REGIONS OF THE WORLD

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DESERT DUST

• WORLD WIDE PICTURE– MAP ON PAGE 1 OF HANDOUT

• SHOWS MAJOR DIRECTIONS AND DISTANCES OF TRANSPORT OF DUST

– SAHARAN DUST TO THE CARIBBEAN– SEE FIGURE 2 OF HANDOUT

– VOLUME OF DUST PER YEAR• ESTIMATED AT 500,000,000 TONS• OFTEN NEGLECTED PART OF TOTAL SEDIMENT

TRANSPORT ON THE EARTH• SUBJECT OF GREATLY INCREASED INTEREST AND

STUDY

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DESERT DUST

• VOLUME (CONT)– WHAT DOES THIS MEAN/

• UNIT COAL TRAINS W/ 120 CARS OF 120 TONS OF COAL EACH

• EACH TRAIN CARRIES 14,400 TONS

• 500,000,000 DIVIDED BY 14,400 = 34,722 TRAINS

• EACH TRAIN 1.26 MILES LONG

• 1.26 TIMES 34,722 = 43,750 MILES

• EARTH CIRCUMFERENCE = 24, 901 MILES

• 1.76 TIMES AROUND THE EQUATOR

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DESERT DUST

• SOURCE AREAS– 36% OF EARTH’S SURFACE (ARID AND SEMI-

ARID REGIONS)• SAHARA• ARABIAN PENINSULA• SUDAN• CHINA• AUSTRALIA• US• ARGENTINA AND CHILE• ETC. – SEE LIST ON P.2 OF HANDOUT

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DESERT DUST

• SOURCES– LARGE DUST STORMS ORIGINATE OVER

ALL DESERTS– LARGE DUST STORMS ARE ALSO

ASSOCIATED WITH AREAS OF SEMI-ARID CLIMATE WHICH PERIODICALLY BECOME ARID – WEST TEXAS, RUSSIAN STEPPE, INDIA

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DESERT DUST

• SOURCES– DUST DEVILS

• SMALL LOCAL FEATURES UP TO WHAT AMOUNT TO TORNADOES

– HABOOBS (Arabic term) – HUGE STORMS LIFTING DUST UP TO 2500 METERS

– DUST STORMS OBSERVED ON SATELLITE IMAGERY

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DESERT DUST

• SOURCES– DUST FROM LOCAL IN SITU

WEATHERING OF ROCKS– ALSO ALLUVIUM FROM WADIS,

ARROYOS, AND PLAYAS– AGRICULTURAL FIELDS– CONSTRUCTION SITES, ETC.

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DESERT DUST

• TRANSPORT– FACTORS THAT INFLUENCE INITIATION OF

DUST MOVEMENT• WIND VELOCITY• SURFACE ROUGHNESS• PARTICLE SIZE• VEGETATION OR LACK THEREOF• MOISTURE CONTENT• TEXTURE• MINERALOGY

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– PARTICLE SIZE• VARIES BUT MOST LESS THAN 50m

• COMMON DUST DEVIL SIZE IS 5-50M

• VERY FINE FRACTION CAN BE HELD IN SUSPENSION FOR QUITE SOME TIME

• SEE GRAIN-SIZE CURVES OF FIGURE 3.

• AEROSOL DUST – WHAT IS IT?– IMPORTANCE

– SIZE FRACTION

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DESERT DUST

• DISTANCE OF TRANSPORT– ACROSS THE ATLANTIC

– GOBI DESERT TO ALASKA

– GOBI DESERT TO CANADA

– AUSTRALIA TO INDIAN OCEAN AND ALSO INTO PACIFIC

– SAHARA DUST TO ISRAEL (25,000,000 TONS?)

– US. DUST FROM WEST TO GEORGIA, 2400 KM.

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DESERT DUST

• MINERALOGY– MAINLY QUARTZ (65%0)– FELDSPAR (0-20%)– CALCIUM AND MAGNESIUM

CARBONATES (UP TO 35%)

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DESERT DUST

• ROLE OF DUST IN GEOLOGIC PROCESSES– OCEAN SEDIMENTS– DESERT VARNISH– CALICHE– SOIL FERTILITY

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DESERT DUST

• DUST AND MAN– PATHOGENS– POLLUTION– DESERTIFICATION– AUTOMOBILE ACCIDENTS– CLIMATIC EFFECTS