Landscape Evolution in Response to Active Tectonics:

The Italian Apennines

Introduction

The Apennines of central and southern Italy form the backbone of lo Stivale. A wealth of tectonic data and relatively homogeneous bedrock lithology makes the Apennines an ideal place to study the effects of tectonic forcing on landscape evolution. This site presents an overview of the continuing work of a collaboration of scientists aiming to record, understand and predict how the earth's surface system responds to a changing tectonic regime.

The adjacent image is a digital elevation model image of central and southern Italy. The field areas of the central and southern Apennines are marked as part of a continuous chain of mountains (brown) extending through the length of 'the boot'.

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Regional Tectonic and Geological Setting

The Apennines are part of the Alpine orogenic system which formed due to convergence of African continental fragments with Eurasia and Subduction of Tethyan ocean crust. The Apennines formed initially as a fold and thrust belt striking NW-SE. Thrusting is still active in the Apennines on the NE side of the range, but ceased in the interior in the Pliocene and crustal extension began c. 3Ma. (oldest dated graben fill sediments c. 2.5Ma). Extension has been related to processes of isostatic rebound, subcrustal, convective mantle flow and/or subducted slab retreat. The normal fault systems that have resulted strike parallel to the axis of “the boot” characterising NE-SW extension. (Roberts & Michetti 2004; Papanikolaou & Roberts 2006)

Figure shows geological structure and surface topography of (a) Central Apennines and (b) Southern Apennines field areas.

Why work in the Apennines?

The Apennines offer an excellent locality to study landscape evolution for a number of reasons:

It is an area with extensive data on fault activity histories:

• There is detailed stratigraphic control on fault initiation time.
• There are good constraints on current fault activity and on long-term and short-term throw rates thanks to earthquake locations studies, palaeoseismic and geomorphic studies, observations of throws across post-glacial (18ky) fault scarps, and geodetic data (Papanikolaou & Roberts 2006).

• Throw rates on faults vary in space and time, providing a wide range of tectonic scenarios to test the fluvial incision laws and characterise the response time of the fluvial system to a tectonic disturbance.
• As a consequence of fault linkage, major faults accelerated and minor fault stopped in the central part of the fault systems, while throw rates remained constant on distal faults: Accelerated faults, decelerated faults, faults with constant throw rate, with throw rates varying between 0 and 2.0 mm/yr as well as unfaulted areas are represented in the Apennines.

• Mesozoic platform carbonate dominate the lithology of the footwalls.
• Lack of bedrock variability is favourable to direct study of tectonic signals in geomorphic systems

• Extensive dating and mapping of glaciation-related sediments and landforms (+ Lago Grande di Monticchio, climate data site).

Objectives

The wealth of tectonic data makes the Italian Apennines an ideal place to study the effects of tectonic forcing on landscape evolution. We are interested in how rivers and debris flow channels flowing across these faults have adjusted to different rates of relative uplift, and crucially, how they have responded to changing rates of fault movement. We need improved field-based constraints on the processes involved here because the fluvial system is the main agent by which changing tectono-climatic conditions are transmitted to the landscape. Amongst others, upland rivers, which tend to incise bedrock, are directly responsible for setting hill-slope gradients, controlling the rate of erosional lowering in mountainous areas and setting the export rate of sediment from active orogens. The project aims to discriminate between a range of competing erosion 'laws' by testing their geological predictions with the geometries observed in rivers crossing faults which have:

1. Moved at a constant rate since faulting initiated
2. Increased in slip rate
3. slowed down through time

In addition we aim to collect an extensive database of fluvial hydraulic scaling parameters (in terms of channel width, slope, median grain-size) to better characterize the geometries of rivers eroding in such active settings.