Transcript impact crater

•Impact craters are geologic structures
formed when a large meteoroid, asteroid
or comet smashes into a planet or a
satellite.
• Often hard to recognize on Earth
because of the effects of weathering and
erosion
•Impact craters are divided into two groups
based on morphology: simple craters and
complex craters.
Simple and Complex Crater
• Simple Craters - are meteorite impact craters of
relatively small diameter, characterized by a uniformly
concave-upward shape and a maximum depth in the
center, and lacking a central uplift.
Simple and Complex Crater
• Complex craters are a type of large impact crater
morphology. The central peak or peak ring of the complex
crater is formed as the initial (transient) deep crater floor
rebounds from the compressional shock of impact.
Slumping of the rim further modifies and enlarges the final
crater.
Parts of an Impact Crater
Parts of an Impact Crater
•Floor — The bottom of a crater, either bowl-shaped or flat, usually below
the level of the surrounding ground.
•Central peaks — Peaks formed in the central area of the floor of a large
crater.
•
•Walls — The interior sides of a crater, usually steep. They may have giant
stair-like terraces that are created by slumping of the walls due to gravity.
•Rim — The edge of the crater. It is elevated above the surrounding terrain
because it is composed of material pushed up at the edge during
excavation.
•Ejecta — Rock material thrown out of the crater area during an impact
event. It is distributed outward from the crater's rim onto the planet's surface
as debris. It can be loose materials or a blanket of debris surrounding the
crater, thinning at the outermost regions.
•Rays — Bright streaks extending away from the crater sometimes for great
distances, composed of ejecta material.
Examples of Terrestrial Impact Craters
•Meteor Crater in Arizona (also know as Barringer Crater) was
the first-recognized terrestrial impact crater. It was identified in
the 1920s by workers who discovered fragments of the meteorite
impactor within the crater itself.
Approximately 1.2 km (0.75 mi.) wide and 200 m (650 ft.) deep.
Created about 50,000 years ago by a 50 m (150 ft.) meteorite.
Examples of Terrestrial Impact Craters
•The Chicxulub crater is an ancient
impact crater buried underneath the
Yucatán Peninsula in Mexico. Its
center is located near the town of
Chicxulub, after which the crater is
named. This caused global
temperatures to plunge near freezing.
Half of the species on Earth became
extinct including the dinosaurs.
•This three-dimensional map of
local gravity and magnetic field
variations shows a multiringed
structure called Chicxulub named
after a village located near its
center.
Examples of Terrestrial Impact Craters
•In Aorounga, Chad, Africa
The impact of an asteroid
or comet several hundred
million years ago left scars
in the landscape that are
still visible in this
spaceborne radar image of
an area in the Sahara
Desert of northern Chad.
The original crater was
buried by sediments, which
were then partially eroded
to reveal the current ringlike appearance.
Examples of Terrestrial Impact Craters
•Wolfe Creek, Australia
Wolfe Creek is a relatively
well-preserved crater that is
partly buried under wind blown
sand. The crater is situated in
the flat desert plains of northcentral Australia. Its crater rim
rises ~25 meters (82 feet)
above the surrounding plains
and the crater floor is ~50
meters (164 feet) below the
rim.
Examples of Terrestrial Impact Craters
•Roter Kamm, South West
Africa/Namibia
Located in the Namibia
Desert, the raised crater rim is
clearly visible against darker
background vegetation.
Target rocks include primarily
Precambrian crystalline rocks
and modest amounts of
younger sedimentary rocks.
Outcrops of impact melt
breccias are found exclusively
on the crater rim. The crater
floor is covered by broad,
shifting sand dunes.