r. a. de hon 2011 swaag, austin, tx crater morphologies in monogenetic volcanic fields of western...

R. A. De Hon

2011 SWAAG, Austin, TX

CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN

NEW MEXICO

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

Ariz

ona

New

Mex

ico

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 XenolithKilbourne Hole, NM

ZUNI SALT LAKE

1 km

Rim deposits

Air Fall Lapilli Tuff, Zuni Salt Lake Maar

Base surgeand Air Fall

Vent Opening Breccia

Breccia contain blocks of subjacent rocks including basement granites and in some localities mantle xenoliths

Base Surge and Air Fall Bedded Deposits

Vent Opening Breccia

RIM DEPOSITS AT KILBOURNE HOLE

Base Surge Beds

Bomb Sag

Accretionary Lapilli

This study

N

100 km

Location of volcanic vent structures in western New Mexico

CHAIN OF CRATERSBANDERA FIELD

Maar

Malpais

CERRO AMERICO

EXAMPLE: CINDER CONE—CERRO AMERICO

Basal Diameter 1 237 metersCrater Diameter 269 Cone Height 118 Crater Depth 41

BANDERA CRATER

EXAMPLE: TUFF RING—BANDERA CRATER

Basal Diameter 1156Crater Diameter 556Rim Height 128Crater Depth 156

HUECO CRATER

EXAMPLE: MAAR—HUECO CRATER

Basal Diameter 1150 metersCrater Diameter 718Rim Height (h) 75Crater Depth (d) 98

dh

La Jolla Maar, Mesa Chivato

1 km

Many maare in the region are characterized by concentration of scrub vegetation on raise tuff rings.

LA JOLLA MAAR, MESA CHIVATO

Basal Diameter 1200Crater Diameter 930Rim Height 15Crater Depth 36

Scoria mound

Tuff Rings

Depth vs. Height

PRISTINE

Tuff Ring

Maar

Cinder cone

VOLCANIC CENTRAL VENT VARIATIONS

1 km

All profiles to same scale.

Variation in size and morphology is chiefly due to the duration of eruptions and volume of material ejected.

Composition of ejecta changes as eruption progresses…

Lava

Scoriaceous cinders

Epiclastic bedded tuff

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 -or-Blew its top?

Floor above surface

Nested Craters

RED HILL MAARMaar with floor cinder cones

Cone filling maar

Rimless depression(erosional remnant

of maar crater)

Renewed activity Pristine Degraded

Cone filling maar Tuff Ring Breached crater

Cone-in-maar Maar Rimless depression

Explosion crater? Cinder cone Scoria Mound

VOLCANIC CENTRAL VENT VARIATIONS

1 km

All profiles to same scale.

Morphological variations corresponding to renewed eruptions or by erosional degradation

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

Mars Volcanic field

THANK YOU