Transcript Landscape change in central Mexico

Landscape change in central Mexico
Anthony Newton
Department of Geography
University of Edinburgh
Introduction
• Long-term research in central Mexico
• Multidisciplinary research
• Multiproxy techniques
Collaborators
• Sarah Metcalfe, Sarah Davis, John Braisby, Nikki
Terret, John Farmer, Bob McCulloch (Edinburgh)
• Phil Barker (Lancaster)
• Richard Telford (Newcastle)
• Georgina Endfield, Sarah O’Hara (Nottingham)
• Melanie Leng (NIGL, Keyworth)
• Gus MacKenzie, Gordon Cook (SUERC, Glasgow)
• Charles Frederick (Sheffield)
• Arturo Chacón and colleagues (UMSNH, Morelia)
• Ana Lillian Martin del Pozzo and colleagues (UNAM,
Mexico City)
Research Themes
• Volcanology and tephrochronology
• Volcanic history
• Impacts on environment and humans
• Dating and correlation
• Climate Change
• Palaeoclimatic record – recent and long-term records
• Human impacts
• Pre- and Post-Hispanic
Central Mexico
C EN T RA L M EX I C O
te
C uitzeo
BASIN OF
MEXICO
m
a
PÁTZCUARO
x ZIRAHUÉN
Jorullo
er
Paricutín
x
oL
ZACAPU
Volcán de
Colima
oc
x
x
Rí
C h a
p a l a
ío
La Piscina
de Yuriria
R
x
ma
M
JUANACATLÁN
zu
Hoya San
Nicolás de
Parangueo
ORIENTAL
UPPER LERMA
x
Nevado de
Toluca
Ajusco
Iztaccíhautl
La Malinche
Popocatépetl
Volcano
Land above 1000 m
x
Lake
Rí
Scale
Small lake
0
100
200 km
o Balsa
s
Pico de
Orizaba
Areas of research
• Basin of Mexico
• Establishment of a tephrochronology
• Upper Lerma (Toluca) Basin
• Establishment of a tephrochronology
• Palaeoenvironmental history
• Impact of eruptions
• Michoacán
•
•
•
•
Establishment of a tephrochronology
Palaeoenvironmental history
Impact of eruptions
Impact of Pre- and Post-Hispanic populations on the
environment
Trans-Mexican Volcanic Belt
C EN T RA L M EX I C O
te
C uitzeo
BASIN OF
MEXICO
m
a
PÁTZCUARO
x ZIRAHUÉN
Jorullo
er
Paricutín
x
oL
ZACAPU
Volcán de
Colima
oc
x
x
Rí
C h a
p a l a
ío
La Piscina
de Yuriria
R
x
ma
M
JUANACATLÁN
zu
Hoya San
Nicolás de
Parangueo
ORIENTAL
UPPER LERMA
x
Nevado de
Toluca
Ajusco
Iztaccíhautl
La Malinche
Popocatépetl
Volcano
Land above 1000 m
x
Lake
Rí
Scale
Small lake
0
100
200 km
o Balsa
s
Pico de
Orizaba
Popocatépetl
Nevado de Toluca
Nevado de Toluca
Paricutín
Volcán de Colima
Basin of Mexico
• To use tephra layers to aid
palaeoenvironmental research
• To establish the hazard posed by
surrounding volcanoes
• 25% of Mexico’s population
•
•
•
•
Popocatépetl (active at the moment)
Iztaccihuatl (active during the Holocene)
Nevado de Toluca (last active c. 11,000 BP)
Numerous cinder cones (Xitle c. 2000 BP)
Basin of Mexico: Results
• Tephras from 10 cores
• Established preliminary
tephrochronological framework
• 2,800 to 34,000 14C years BP
• Nevado de Toluca and Popocatépetl could
pose significant risks
• Dating and integration with archaeology
Cuicuilco and Xitle Lava
Toluca Basin
• To use tephra layers to aid palaeoenvironmental
research
• To increase volcanological knowledge of the area
• Previously no precise analyses of tephra layers
• Area dominated by the Nevado de Toluca and
cinder cone activity
Toluca Basin Tephrastratigraphy
Results
• 11 late Pleistocene and Holocene tephra
layers analysed
• Tephrochronological framework
established
• New tephra layers found
• Established link to the Basin of Mexico
Michoacán
C EN T RA L M EX I C O
te
C uitzeo
BASIN OF
MEXICO
m
a
PÁTZCUARO
x ZIRAHUÉN
Jorullo
er
Paricutín
x
oL
ZACAPU
Volcán de
Colima
oc
x
x
Rí
C h a
p a l a
ío
La Piscina
de Yuriria
R
x
ma
M
JUANACATLÁN
zu
Hoya San
Nicolás de
Parangueo
ORIENTAL
UPPER LERMA
x
Nevado de
Toluca
Ajusco
Iztaccíhautl
La Malinche
Popocatépetl
Volcano
Land above 1000 m
x
Lake
Rí
Scale
Small lake
0
100
200 km
o Balsa
s
Pico de
Orizaba
Michoacán-Guanajuato Volcanic Field
• 40,000 km2 dominated by cinder cones
and shield volcanoes
• 900 monogenetic cinder cones
• 300 monogenetic shield volcanoes
• two stratovolcanoes
• Average of two eruptions per 1000 years
• 70-80 cones less than 40,000 years old
• Paricutín (1943 - 1952)
• Jorullo (1759-1774)
Tephra impact on lakes
• Analyse and date the major tephras
• Assess the response of diatom
assemblages to these tephras
• Develop a response model
• Consider the impact of tephra on long
term environmental reconstruction
Methods
• Cores and sections of lake sediments and
tephra
• Microprobe analyses of volcanic glass
• Dating using tephrochronology,
and historical records
14C, 210Pb
• High resolution diatom analysis in the
context of long-term climate change
Conclusions
• Tephras < 1 cm rarely show a response
• Changes in diatom assemblages short-lived (150200 years)
• There is no simple relationship between the Si
content of a tephra and a diatom response
• Available phosphorus varies with tephra inputs
• Historical tephras show little impact
• Tephras from cinder cones unlikely to affect longterm lake evolution
Exploring ‘The Pristine Myth’
• Did the indigenous population alter or
degrade their environment?
• What was the nature of the environmental
impact of European settlers?
• What are the implications for
contemporary landscape and resource
management?
Pre-Classic: Cuicuilco, Basin of Mexico
(< 100 BC)
Classic: Teotihuacán, Basin of Mexico
(100 BC – 650-750 AD)
Teotihuacán
Teotihuacán
Teotihuacán
Post-Classic: Tula,
Basin of Mexico
Toltecs (950-1150 AD)
Post-Classic: Cuicuilco, Basin of Mexico
Mexica (Aztecs) 1325-1521AD
Post-Classic: Teotenango, Toluca Basin
Matlatzinca 600-1560 AD
Teotenango
Post-Classic: Tzintzuntzan, Patzcuaro
Tarascans 1200-1530
Modern,
Zacapu
Chimampas
Colonial 1521
Independence 1821
Tarascan Society
Tarascan Society
• Purépecha ruled by Cazonci
• Second most important after Aztec Empire
• Occupied roughly area of the state of
Michoacán
• At time of Spanish conquest the capital at
Tzinztuntzan, Patzcuaro
• 25,000 - 30,000 to 100,000 inhabitants
Tarascan Society
• Population of Patzcuaro area imported
food
• Metallurgical Activity
• Gold and copper
• Copper
• Sculpture and ceramics
• Relación de Michoacán (1540-41)
The Spanish Conquest
The Spanish Conquest
• First Spanish Soldier - 23 February 1521
• Tried to remain autonomous from Spanish
• Used as a base by Spanish
• Cazonci executed 14 February 1530
Methods
• Palaeoenvironmental records
• Archives
• Archaeology
• Modern environmental studies
Archive Sources
• Archivo General de la Nacion
• Tierras
• land disputes – geographical descriptions,
sometimes maps)
• Inspeccion Occular de Michoacán (1791)
»
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Description of all towns and villages
Ecclesiastical details
Population
Economic activity
Inspeccion Occular de Michoacán
• Santa Clara del Cobre (near Zirahuén)
“… 8 copper foundries each with a work force of
between 30 to 40.”
• Lago de Zirahuén
“… with crystal water, healthy and surrounded by
peaks covered in pine trees, productive white
fish … smaller than those in Laguna de
Pazquaro, but superior in quality”
• Arocutin
“… situated on sterile, high, rough badlands, with
miserable huts of stakes or adobe … full of
uninhabited ruins.”
20,000 year record: Pátzcuaro
1000 year record: Zirahuén
Zirahuén Conclusions
• Pre-Hispanic soil erosion
• Catchment stability during the early Colonial
period
• Accelerated soil erosion, pollution from copper
smelting and nutrient enrichment of lake waters
have occurred since the mid-18th century
• A rapid response to recent land use change.
3000 year record: Zacapu
Continuing Research
• Interpret archive and palaeoenvironmental results
• Improve dating of recent sediments and volcanic
deposits
• Work with those studying modern-day processes
– decision makers
• Link on-shore and off-shore sediment sequences
• Palaeoclimate studies
• Continue multidisciplinary research