Transcript Crater Morphologies

CRATER MORPHOLOGIES IN MONOGENETIC
VOLCANIC FIELDS OF WESTERN
NEW MEXICO
R. A. De Hon
2011 SWAAG, Austin, TX
THIS PRESENTATION
• As title states…
Morphology of landforms in three monogenic volcanic fields in
western New Mexico
• Specifically, the morphology of…
Maar craters
Tuff rings
Cinder cones
and modification of these forms
• Located in …
Red Hill-Quemado Volcanic Field
Bandera Volcanic Field
Mt. Taylor-Mesa Chivato Volcanic Field
Mesa Chivato
Bandera
(Malpias)
Red Hill
MAAR CRATERS
WITH SPECIAL ATTENTION TO MAAR CRATERS
• Maar craters are formed when magma encounters groundwater.
The resultant venting to the surface excavates a bowl-shaped
pit surrounded by a tuff ring that resembles a meteorite crater.
• The term maar comes from a Franconian dialect for lake derived
from the Latin “mare” (sea).
• In the type locality—the Efiel Region of Germany— the craters
extend below the water table and are occupied by lakes.
• Maar craters range in size from a few hundred meters to several
kilometers in diameter.
• Their eruptive history consists of repeated venting over a period
of weeks or months.
ULTIMATE OBJECTIVES
• Volcanic morphometry with attention to craters
and their modification by later eruption or
erosion
• Early ejecta as sampling of subjacent rock
materials
• Application to Martain volcanic craters.
WHY SHOULD YOU CARE?
• The earliest ejecta in maar craters provide a sampling
of subjacent strata.
• At some localities the ejecta incudes mantle xenoliths.
Mantle Xenolith
Kilbourne Hole, NM
ZUNI SALT LAKE
1 km
Rim deposits
Air Fall Lapilli Tuff, Zuni Salt Lake Maar
Base surge
and Air Fall
Vent Opening
Breccia
Breccia contain
blocks of subjacent
rocks including
basement granites
and in some
localities mantle
xenoliths
RIM DEPOSITS AT KILBOURNE HOLE
Base Surge and Air Fall
Bedded Deposits
Vent Opening
Breccia
Base Surge Beds
Accretionary Lapilli
Bomb Sag
This study
N
100 km
Location of volcanic vent structures in western New Mexico
Malpais
CHAIN OF CRATERS
BANDERA FIELD
Maar
CERRO AMERICO
EXAMPLE: CINDER CONE—CERRO AMERICO
Basal Diameter 1 237 meters
Crater Diameter
269
Cone Height
118
Crater Depth
41
BANDERA CRATER
EXAMPLE: TUFF RING—BANDERA CRATER
Basal Diameter
Crater Diameter
Rim Height
Crater Depth
1156
556
128
156
HUECO CRATER
EXAMPLE: MAAR—HUECO CRATER
d
h
Basal Diameter 1150 meters
Crater Diameter 718
Rim Height (h)
75
Crater Depth (d)
98
La Jolla Maar, Mesa Chivato
Many maare in the region are
characterized by concentration of
scrub vegetation on raise tuff
rings.
1 km
LA JOLLA MAAR, MESA CHIVATO
Basal Diameter 1200
Crater Diameter 930
Rim Height
15
Crater Depth
36
Scoria mound
Depth vs. Height
VOLCANIC CENTRAL VENT VARIATIONS
PRISTINE
Composition of ejecta changes
as eruption progresses…
Lava
Variation in size and
morphology is chiefly due
to the duration of eruptions
and volume of material
ejected.
Cinder cone
Scoriaceous cinders
Tuff Ring
Epiclastic bedded tuff
Maar
1 km
All profiles to same scale.
Early xenolith-rich breccia
VENT MORPHOLOGY
• Magma and ground-water interaction
• Duration of activity
• Accidental ejecta
• Pyroclastic
• Lava
• Resistance of country rock
• Slumping during eruptive phase
• Degradation following eruption
Highly eroded
-orBlew its top?
Floor above surface
Nested Craters
RED HILL MAAR
Maar with floor
cinder cones
Cone filling maar
Rimless
depression
(erosional remnant
of maar crater)
VOLCANIC CENTRAL VENT VARIATIONS
Renewed activity
Explosion crater?
Pristine
Cinder cone
Cone filling maar
Tuff Ring
Cone-in-maar
Maar
Degraded
Scoria Mound
Breached crater
Rimless depression
1 km
All profiles to same scale.
Morphological variations corresponding to renewed eruptions or by erosional
SO, WHAT? THE POINT IS…
• Earliest maar ejecta provides a sample of substrate
materials.
• Those early materials may be preserved in a variety for
subsequent volcanic structures.
• Someday…maar craters and their variants will be
important sites to visit on Mars.
CREDITS
PREVIOUS WORKERS IN WESTERN NEW MEXICO VOLCANIC FIELDS
• Jayne C. Aubele
• Larry S. Crumpler
• A. W. Laughlin
• P. W. Lipman
• C. Maxwell
• And many others
THANK YOU
Mars Volcanic field